Roll Protobuf r415:r423.

third_party/protobuf/src/google/protobuf/compiler/plugin.pb.cc

Index: third_party/protobuf/src/google/protobuf/compiler/plugin.pb.cc
diff --git a/third_party/protobuf/src/google/protobuf/compiler/plugin.pb.cc b/third_party/protobuf/src/google/protobuf/compiler/plugin.pb.cc
index 1d27b4144b93996118732e995afec67ee60ae8d7..c95618848f3fa9d495eb358f2e9db16fa55bdb52 100644
--- a/third_party/protobuf/src/google/protobuf/compiler/plugin.pb.cc
+++ b/third_party/protobuf/src/google/protobuf/compiler/plugin.pb.cc
@@ -243,7 +243,8 @@ bool CodeGeneratorRequest::MergePartialFromCodedStream(
           DO_(::google::protobuf::internal::WireFormatLite::ReadString(
                 input, this->add_file_to_generate()));
           ::google::protobuf::internal::WireFormat::VerifyUTF8String(
-            this->file_to_generate(0).data(), this->file_to_generate(0).length(),
+            this->file_to_generate(this->file_to_generate_size() - 1).data(),
+            this->file_to_generate(this->file_to_generate_size() - 1).length(),
             ::google::protobuf::internal::WireFormat::PARSE);
         } else {
           goto handle_uninterpreted;