Add plugins at the time of static initialization

src/cpp/server/server_builder.cc

diff --git a/src/cpp/server/server_builder.cc b/src/cpp/server/server_builder.cc
index 5dc73ed..b6e48ef 100644
--- a/src/cpp/server/server_builder.cc
+++ b/src/cpp/server/server_builder.cc
@@ -41,9 +41,21 @@
 
 namespace grpc {
 
+static std::vector<std::unique_ptr<ServerBuilderPlugin> (*)()>* plugin_list;
+static gpr_once once_init_plugin_list = GPR_ONCE_INIT;
+
+static void do_plugin_list_init(void) {
+  plugin_list = new std::vector<std::unique_ptr<ServerBuilderPlugin> (*)()>();
+}
+
 ServerBuilder::ServerBuilder()
     : max_message_size_(-1), generic_service_(nullptr) {
   grpc_compression_options_init(&compression_options_);
+  gpr_once_init(&once_init_plugin_list, do_plugin_list_init);
+  for (auto factory : (*plugin_list)) {
+    std::unique_ptr<ServerBuilderPlugin> plugin = factory();
+    plugins_[plugin->name()] = std::move(plugin);
+  }
 }
 
 std::unique_ptr<ServerCompletionQueue> ServerBuilder::AddCompletionQueue() {
@@ -156,4 +168,10 @@
   return server;
 }
 
+void ServerBuilder::InternalAddPluginFactory(
+    std::unique_ptr<ServerBuilderPlugin> (*CreatePlugin)()) {
+  gpr_once_init(&once_init_plugin_list, do_plugin_list_init);
+  (*plugin_list).push_back(CreatePlugin);
+}
+
 }  // namespace grpc