alts: move alts protos to match proto package

diff --git a/alts/BUILD.bazel b/alts/BUILD.bazel
index ca72e1d..aaa3e34 100644
--- a/alts/BUILD.bazel
+++ b/alts/BUILD.bazel
@@ -45,23 +45,23 @@
 # bazel only accepts proto import with absolute path.
 genrule(
     name = "protobuf_imports",
-    srcs = glob(["src/main/proto/*.proto"]),
+    srcs = glob(["src/main/proto/grpc/gcp/*.proto"]),
     outs = [
-        "protobuf_out/altscontext.proto",
-        "protobuf_out/handshaker.proto",
-        "protobuf_out/transport_security_common.proto",
+        "protobuf_out/grpc/gcp/altscontext.proto",
+        "protobuf_out/grpc/gcp/handshaker.proto",
+        "protobuf_out/grpc/gcp/transport_security_common.proto",
     ],
     cmd = "for fname in $(SRCS); do " +
           "sed 's,import \",import \"alts/protobuf_out/,g' $$fname > " +
-          "$(@D)/protobuf_out/$$(basename $$fname); done",
+          "$(@D)/protobuf_out/grpc/gcp/$$(basename $$fname); done",
 )
 
 proto_library(
     name = "handshaker_proto",
     srcs = [
-        "protobuf_out/altscontext.proto",
-        "protobuf_out/handshaker.proto",
-        "protobuf_out/transport_security_common.proto",
+        "protobuf_out/grpc/gcp/altscontext.proto",
+        "protobuf_out/grpc/gcp/handshaker.proto",
+        "protobuf_out/grpc/gcp/transport_security_common.proto",
     ],
 )
 
diff --git a/alts/src/generated/main/grpc/io/grpc/alts/internal/HandshakerServiceGrpc.java b/alts/src/generated/main/grpc/io/grpc/alts/internal/HandshakerServiceGrpc.java
index 58789fb..47c3396 100644
--- a/alts/src/generated/main/grpc/io/grpc/alts/internal/HandshakerServiceGrpc.java
+++ b/alts/src/generated/main/grpc/io/grpc/alts/internal/HandshakerServiceGrpc.java
@@ -19,7 +19,7 @@
  */
 @javax.annotation.Generated(
     value = "by gRPC proto compiler",
-    comments = "Source: handshaker.proto")
+    comments = "Source: grpc/gcp/handshaker.proto")
 public final class HandshakerServiceGrpc {
 
   private HandshakerServiceGrpc() {}
diff --git a/alts/src/generated/main/java/io/grpc/alts/internal/Altscontext.java b/alts/src/generated/main/java/io/grpc/alts/internal/Altscontext.java
index a645171..d036c2e 100644
--- a/alts/src/generated/main/java/io/grpc/alts/internal/Altscontext.java
+++ b/alts/src/generated/main/java/io/grpc/alts/internal/Altscontext.java
@@ -1,5 +1,5 @@
 // Generated by the protocol buffer compiler.  DO NOT EDIT!
-// source: altscontext.proto
+// source: grpc/gcp/altscontext.proto
 
 package io.grpc.alts.internal;
 
@@ -1490,15 +1490,15 @@
       descriptor;
   static {
     java.lang.String[] descriptorData = {
-      "\n\021altscontext.proto\022\010grpc.gcp\032\037transport" +
-      "_security_common.proto\"\354\001\n\013AltsContext\022\034" +
-      "\n\024application_protocol\030\001 \001(\t\022\027\n\017record_p" +
-      "rotocol\030\002 \001(\t\022/\n\016security_level\030\003 \001(\0162\027." +
-      "grpc.gcp.SecurityLevel\022\034\n\024peer_service_a" +
-      "ccount\030\004 \001(\t\022\035\n\025local_service_account\030\005 " +
-      "\001(\t\0228\n\021peer_rpc_versions\030\006 \001(\0132\035.grpc.gc" +
-      "p.RpcProtocolVersionsB\027\n\025io.grpc.alts.in" +
-      "ternalb\006proto3"
+      "\n\032grpc/gcp/altscontext.proto\022\010grpc.gcp\032(" +
+      "grpc/gcp/transport_security_common.proto" +
+      "\"\354\001\n\013AltsContext\022\034\n\024application_protocol" +
+      "\030\001 \001(\t\022\027\n\017record_protocol\030\002 \001(\t\022/\n\016secur" +
+      "ity_level\030\003 \001(\0162\027.grpc.gcp.SecurityLevel" +
+      "\022\034\n\024peer_service_account\030\004 \001(\t\022\035\n\025local_" +
+      "service_account\030\005 \001(\t\0228\n\021peer_rpc_versio" +
+      "ns\030\006 \001(\0132\035.grpc.gcp.RpcProtocolVersionsB" +
+      "\027\n\025io.grpc.alts.internalb\006proto3"
     };
     com.google.protobuf.Descriptors.FileDescriptor.InternalDescriptorAssigner assigner =
         new com.google.protobuf.Descriptors.FileDescriptor.    InternalDescriptorAssigner() {
diff --git a/alts/src/generated/main/java/io/grpc/alts/internal/Handshaker.java b/alts/src/generated/main/java/io/grpc/alts/internal/Handshaker.java
index 03d7887..51dc505 100644
--- a/alts/src/generated/main/java/io/grpc/alts/internal/Handshaker.java
+++ b/alts/src/generated/main/java/io/grpc/alts/internal/Handshaker.java
@@ -1,5 +1,5 @@
 // Generated by the protocol buffer compiler.  DO NOT EDIT!
-// source: handshaker.proto
+// source: grpc/gcp/handshaker.proto
 
 package io.grpc.alts.internal;
 
@@ -13179,60 +13179,60 @@
       descriptor;
   static {
     java.lang.String[] descriptorData = {
-      "\n\020handshaker.proto\022\010grpc.gcp\032\037transport_" +
-      "security_common.proto\"Y\n\010Endpoint\022\022\n\nip_" +
-      "address\030\001 \001(\t\022\014\n\004port\030\002 \001(\005\022+\n\010protocol\030" +
-      "\003 \001(\0162\031.grpc.gcp.NetworkProtocol\"K\n\010Iden" +
-      "tity\022\031\n\017service_account\030\001 \001(\tH\000\022\022\n\010hostn" +
-      "ame\030\002 \001(\tH\000B\020\n\016identity_oneof\"\222\003\n\027StartC" +
-      "lientHandshakeReq\022@\n\033handshake_security_" +
-      "protocol\030\001 \001(\0162\033.grpc.gcp.HandshakeProto" +
-      "col\022\035\n\025application_protocols\030\002 \003(\t\022\030\n\020re" +
-      "cord_protocols\030\003 \003(\t\022-\n\021target_identitie" +
-      "s\030\004 \003(\0132\022.grpc.gcp.Identity\022*\n\016local_ide" +
-      "ntity\030\005 \001(\0132\022.grpc.gcp.Identity\022*\n\016local" +
-      "_endpoint\030\006 \001(\0132\022.grpc.gcp.Endpoint\022+\n\017r" +
-      "emote_endpoint\030\007 \001(\0132\022.grpc.gcp.Endpoint" +
-      "\022\023\n\013target_name\030\010 \001(\t\0223\n\014rpc_versions\030\t " +
-      "\001(\0132\035.grpc.gcp.RpcProtocolVersions\"c\n\031Se" +
-      "rverHandshakeParameters\022\030\n\020record_protoc" +
-      "ols\030\001 \003(\t\022,\n\020local_identities\030\002 \003(\0132\022.gr" +
-      "pc.gcp.Identity\"\223\003\n\027StartServerHandshake" +
-      "Req\022\035\n\025application_protocols\030\001 \003(\t\022X\n\024ha" +
-      "ndshake_parameters\030\002 \003(\0132:.grpc.gcp.Star" +
-      "tServerHandshakeReq.HandshakeParametersE" +
-      "ntry\022\020\n\010in_bytes\030\003 \001(\014\022*\n\016local_endpoint" +
-      "\030\004 \001(\0132\022.grpc.gcp.Endpoint\022+\n\017remote_end" +
-      "point\030\005 \001(\0132\022.grpc.gcp.Endpoint\0223\n\014rpc_v" +
-      "ersions\030\006 \001(\0132\035.grpc.gcp.RpcProtocolVers" +
-      "ions\032_\n\030HandshakeParametersEntry\022\013\n\003key\030" +
-      "\001 \001(\005\0222\n\005value\030\002 \001(\0132#.grpc.gcp.ServerHa" +
-      "ndshakeParameters:\0028\001\"+\n\027NextHandshakeMe" +
-      "ssageReq\022\020\n\010in_bytes\030\001 \001(\014\"\305\001\n\rHandshake" +
-      "rReq\0229\n\014client_start\030\001 \001(\0132!.grpc.gcp.St" +
-      "artClientHandshakeReqH\000\0229\n\014server_start\030" +
-      "\002 \001(\0132!.grpc.gcp.StartServerHandshakeReq" +
-      "H\000\0221\n\004next\030\003 \001(\0132!.grpc.gcp.NextHandshak" +
-      "eMessageReqH\000B\013\n\treq_oneof\"\207\002\n\020Handshake" +
-      "rResult\022\034\n\024application_protocol\030\001 \001(\t\022\027\n" +
-      "\017record_protocol\030\002 \001(\t\022\020\n\010key_data\030\003 \001(\014" +
-      "\022)\n\rpeer_identity\030\004 \001(\0132\022.grpc.gcp.Ident" +
-      "ity\022*\n\016local_identity\030\005 \001(\0132\022.grpc.gcp.I" +
-      "dentity\022\031\n\021keep_channel_open\030\006 \001(\010\0228\n\021pe" +
-      "er_rpc_versions\030\007 \001(\0132\035.grpc.gcp.RpcProt" +
-      "ocolVersions\"1\n\020HandshakerStatus\022\014\n\004code" +
-      "\030\001 \001(\r\022\017\n\007details\030\002 \001(\t\"\224\001\n\016HandshakerRe" +
-      "sp\022\022\n\nout_frames\030\001 \001(\014\022\026\n\016bytes_consumed" +
-      "\030\002 \001(\r\022*\n\006result\030\003 \001(\0132\032.grpc.gcp.Handsh" +
-      "akerResult\022*\n\006status\030\004 \001(\0132\032.grpc.gcp.Ha" +
-      "ndshakerStatus*J\n\021HandshakeProtocol\022\"\n\036H" +
-      "ANDSHAKE_PROTOCOL_UNSPECIFIED\020\000\022\007\n\003TLS\020\001" +
-      "\022\010\n\004ALTS\020\002*E\n\017NetworkProtocol\022 \n\034NETWORK" +
-      "_PROTOCOL_UNSPECIFIED\020\000\022\007\n\003TCP\020\001\022\007\n\003UDP\020" +
-      "\0022[\n\021HandshakerService\022F\n\013DoHandshake\022\027." +
-      "grpc.gcp.HandshakerReq\032\030.grpc.gcp.Handsh" +
-      "akerResp\"\000(\0010\001B\027\n\025io.grpc.alts.internalb" +
-      "\006proto3"
+      "\n\031grpc/gcp/handshaker.proto\022\010grpc.gcp\032(g" +
+      "rpc/gcp/transport_security_common.proto\"" +
+      "Y\n\010Endpoint\022\022\n\nip_address\030\001 \001(\t\022\014\n\004port\030" +
+      "\002 \001(\005\022+\n\010protocol\030\003 \001(\0162\031.grpc.gcp.Netwo" +
+      "rkProtocol\"K\n\010Identity\022\031\n\017service_accoun" +
+      "t\030\001 \001(\tH\000\022\022\n\010hostname\030\002 \001(\tH\000B\020\n\016identit" +
+      "y_oneof\"\222\003\n\027StartClientHandshakeReq\022@\n\033h" +
+      "andshake_security_protocol\030\001 \001(\0162\033.grpc." +
+      "gcp.HandshakeProtocol\022\035\n\025application_pro" +
+      "tocols\030\002 \003(\t\022\030\n\020record_protocols\030\003 \003(\t\022-" +
+      "\n\021target_identities\030\004 \003(\0132\022.grpc.gcp.Ide" +
+      "ntity\022*\n\016local_identity\030\005 \001(\0132\022.grpc.gcp" +
+      ".Identity\022*\n\016local_endpoint\030\006 \001(\0132\022.grpc" +
+      ".gcp.Endpoint\022+\n\017remote_endpoint\030\007 \001(\0132\022" +
+      ".grpc.gcp.Endpoint\022\023\n\013target_name\030\010 \001(\t\022" +
+      "3\n\014rpc_versions\030\t \001(\0132\035.grpc.gcp.RpcProt" +
+      "ocolVersions\"c\n\031ServerHandshakeParameter" +
+      "s\022\030\n\020record_protocols\030\001 \003(\t\022,\n\020local_ide" +
+      "ntities\030\002 \003(\0132\022.grpc.gcp.Identity\"\223\003\n\027St" +
+      "artServerHandshakeReq\022\035\n\025application_pro" +
+      "tocols\030\001 \003(\t\022X\n\024handshake_parameters\030\002 \003" +
+      "(\0132:.grpc.gcp.StartServerHandshakeReq.Ha" +
+      "ndshakeParametersEntry\022\020\n\010in_bytes\030\003 \001(\014" +
+      "\022*\n\016local_endpoint\030\004 \001(\0132\022.grpc.gcp.Endp" +
+      "oint\022+\n\017remote_endpoint\030\005 \001(\0132\022.grpc.gcp" +
+      ".Endpoint\0223\n\014rpc_versions\030\006 \001(\0132\035.grpc.g" +
+      "cp.RpcProtocolVersions\032_\n\030HandshakeParam" +
+      "etersEntry\022\013\n\003key\030\001 \001(\005\0222\n\005value\030\002 \001(\0132#" +
+      ".grpc.gcp.ServerHandshakeParameters:\0028\001\"" +
+      "+\n\027NextHandshakeMessageReq\022\020\n\010in_bytes\030\001" +
+      " \001(\014\"\305\001\n\rHandshakerReq\0229\n\014client_start\030\001" +
+      " \001(\0132!.grpc.gcp.StartClientHandshakeReqH" +
+      "\000\0229\n\014server_start\030\002 \001(\0132!.grpc.gcp.Start" +
+      "ServerHandshakeReqH\000\0221\n\004next\030\003 \001(\0132!.grp" +
+      "c.gcp.NextHandshakeMessageReqH\000B\013\n\treq_o" +
+      "neof\"\207\002\n\020HandshakerResult\022\034\n\024application" +
+      "_protocol\030\001 \001(\t\022\027\n\017record_protocol\030\002 \001(\t" +
+      "\022\020\n\010key_data\030\003 \001(\014\022)\n\rpeer_identity\030\004 \001(" +
+      "\0132\022.grpc.gcp.Identity\022*\n\016local_identity\030" +
+      "\005 \001(\0132\022.grpc.gcp.Identity\022\031\n\021keep_channe" +
+      "l_open\030\006 \001(\010\0228\n\021peer_rpc_versions\030\007 \001(\0132" +
+      "\035.grpc.gcp.RpcProtocolVersions\"1\n\020Handsh" +
+      "akerStatus\022\014\n\004code\030\001 \001(\r\022\017\n\007details\030\002 \001(" +
+      "\t\"\224\001\n\016HandshakerResp\022\022\n\nout_frames\030\001 \001(\014" +
+      "\022\026\n\016bytes_consumed\030\002 \001(\r\022*\n\006result\030\003 \001(\013" +
+      "2\032.grpc.gcp.HandshakerResult\022*\n\006status\030\004" +
+      " \001(\0132\032.grpc.gcp.HandshakerStatus*J\n\021Hand" +
+      "shakeProtocol\022\"\n\036HANDSHAKE_PROTOCOL_UNSP" +
+      "ECIFIED\020\000\022\007\n\003TLS\020\001\022\010\n\004ALTS\020\002*E\n\017NetworkP" +
+      "rotocol\022 \n\034NETWORK_PROTOCOL_UNSPECIFIED\020" +
+      "\000\022\007\n\003TCP\020\001\022\007\n\003UDP\020\0022[\n\021HandshakerService" +
+      "\022F\n\013DoHandshake\022\027.grpc.gcp.HandshakerReq" +
+      "\032\030.grpc.gcp.HandshakerResp\"\000(\0010\001B\027\n\025io.g" +
+      "rpc.alts.internalb\006proto3"
     };
     com.google.protobuf.Descriptors.FileDescriptor.InternalDescriptorAssigner assigner =
         new com.google.protobuf.Descriptors.FileDescriptor.    InternalDescriptorAssigner() {
diff --git a/alts/src/generated/main/java/io/grpc/alts/internal/TransportSecurityCommon.java b/alts/src/generated/main/java/io/grpc/alts/internal/TransportSecurityCommon.java
index 65b56e3..beb3839 100644
--- a/alts/src/generated/main/java/io/grpc/alts/internal/TransportSecurityCommon.java
+++ b/alts/src/generated/main/java/io/grpc/alts/internal/TransportSecurityCommon.java
@@ -1,5 +1,5 @@
 // Generated by the protocol buffer compiler.  DO NOT EDIT!
-// source: transport_security_common.proto
+// source: grpc/gcp/transport_security_common.proto
 
 package io.grpc.alts.internal;
 
@@ -1571,15 +1571,16 @@
       descriptor;
   static {
     java.lang.String[] descriptorData = {
-      "\n\037transport_security_common.proto\022\010grpc." +
-      "gcp\"\276\001\n\023RpcProtocolVersions\022>\n\017max_rpc_v" +
-      "ersion\030\001 \001(\0132%.grpc.gcp.RpcProtocolVersi" +
-      "ons.Version\022>\n\017min_rpc_version\030\002 \001(\0132%.g" +
-      "rpc.gcp.RpcProtocolVersions.Version\032\'\n\007V" +
-      "ersion\022\r\n\005major\030\001 \001(\r\022\r\n\005minor\030\002 \001(\r*Q\n\r" +
-      "SecurityLevel\022\021\n\rSECURITY_NONE\020\000\022\022\n\016INTE" +
-      "GRITY_ONLY\020\001\022\031\n\025INTEGRITY_AND_PRIVACY\020\002B" +
-      "\027\n\025io.grpc.alts.internalb\006proto3"
+      "\n(grpc/gcp/transport_security_common.pro" +
+      "to\022\010grpc.gcp\"\276\001\n\023RpcProtocolVersions\022>\n\017" +
+      "max_rpc_version\030\001 \001(\0132%.grpc.gcp.RpcProt" +
+      "ocolVersions.Version\022>\n\017min_rpc_version\030" +
+      "\002 \001(\0132%.grpc.gcp.RpcProtocolVersions.Ver" +
+      "sion\032\'\n\007Version\022\r\n\005major\030\001 \001(\r\022\r\n\005minor\030" +
+      "\002 \001(\r*Q\n\rSecurityLevel\022\021\n\rSECURITY_NONE\020" +
+      "\000\022\022\n\016INTEGRITY_ONLY\020\001\022\031\n\025INTEGRITY_AND_P" +
+      "RIVACY\020\002B\027\n\025io.grpc.alts.internalb\006proto" +
+      "3"
     };
     com.google.protobuf.Descriptors.FileDescriptor.InternalDescriptorAssigner assigner =
         new com.google.protobuf.Descriptors.FileDescriptor.    InternalDescriptorAssigner() {
diff --git a/alts/src/main/proto/altscontext.proto b/alts/src/main/proto/grpc/gcp/altscontext.proto
similarity index 92%
rename from alts/src/main/proto/altscontext.proto
rename to alts/src/main/proto/grpc/gcp/altscontext.proto
index 823d4a0..30cc082 100644
--- a/alts/src/main/proto/altscontext.proto
+++ b/alts/src/main/proto/grpc/gcp/altscontext.proto
@@ -1,6 +1,6 @@
 syntax = "proto3";
 
-import "transport_security_common.proto";
+import "grpc/gcp/transport_security_common.proto";
 
 package grpc.gcp;
 
diff --git a/alts/src/main/proto/handshaker.proto b/alts/src/main/proto/grpc/gcp/handshaker.proto
similarity index 98%
rename from alts/src/main/proto/handshaker.proto
rename to alts/src/main/proto/grpc/gcp/handshaker.proto
index 9350f63..feffe1f 100644
--- a/alts/src/main/proto/handshaker.proto
+++ b/alts/src/main/proto/grpc/gcp/handshaker.proto
@@ -1,6 +1,6 @@
 syntax = "proto3";
 
-import "transport_security_common.proto";
+import "grpc/gcp/transport_security_common.proto";
 
 package grpc.gcp;
 
diff --git a/alts/src/main/proto/transport_security_common.proto b/alts/src/main/proto/grpc/gcp/transport_security_common.proto
similarity index 100%
rename from alts/src/main/proto/transport_security_common.proto
rename to alts/src/main/proto/grpc/gcp/transport_security_common.proto