Enable payload v2.

Switch the preferred payload major version to 2.

Bug: 23694580
Test: Deployed signed and unsigned payload to a device.

Change-Id: Ib338883510c1c8ddaad3e4c77a769799ee058b64

delta_performer.cc

diff --git a/delta_performer.cc b/delta_performer.cc
index 0d335a8..eac4259 100644
--- a/delta_performer.cc
+++ b/delta_performer.cc
@@ -64,7 +64,7 @@
 const uint64_t DeltaPerformer::kDeltaManifestSizeSize = 8;
 const uint64_t DeltaPerformer::kDeltaMetadataSignatureSizeSize = 4;
 const uint64_t DeltaPerformer::kMaxPayloadHeaderSize = 24;
-const uint64_t DeltaPerformer::kSupportedMajorPayloadVersion = 1;
+const uint64_t DeltaPerformer::kSupportedMajorPayloadVersion = 2;
 const uint32_t DeltaPerformer::kSupportedMinorPayloadVersion = 2;
 
 const unsigned DeltaPerformer::kProgressLogMaxChunks = 10;
@@ -418,7 +418,8 @@
     // switch big endian to host
     major_payload_version_ = be64toh(major_payload_version_);
 
-    if (major_payload_version_ != supported_major_version_) {
+    if (major_payload_version_ != supported_major_version_ &&
+        major_payload_version_ != kChromeOSMajorPayloadVersion) {
       LOG(ERROR) << "Bad payload format -- unsupported payload version: "
           << major_payload_version_;
       *error = ErrorCode::kUnsupportedMajorPayloadVersion;

update_engine.conf

diff --git a/update_engine.conf b/update_engine.conf
index dea31e4..981887d 100644
--- a/update_engine.conf
+++ b/update_engine.conf
@@ -1,2 +1,2 @@
-PAYLOAD_MAJOR_VERSION=1
+PAYLOAD_MAJOR_VERSION=2
 PAYLOAD_MINOR_VERSION=2