Pull new version of protobuf sources.

third_party/protobuf/src/google/protobuf/compiler/subprocess.cc

Index: third_party/protobuf/src/google/protobuf/compiler/subprocess.cc
diff --git a/third_party/protobuf/src/google/protobuf/compiler/subprocess.cc b/third_party/protobuf/src/google/protobuf/compiler/subprocess.cc
index cc63e40d3c102100f580ab54d9114c658401a352..a3cff1f8b80296aedeaf9ac0cd0e872c9ccc9b4f 100644
--- a/third_party/protobuf/src/google/protobuf/compiler/subprocess.cc
+++ b/third_party/protobuf/src/google/protobuf/compiler/subprocess.cc
@@ -1,6 +1,6 @@
 // Protocol Buffers - Google's data interchange format
 // Copyright 2008 Google Inc.  All rights reserved.
-// http://code.google.com/p/protobuf/
+// https://developers.google.com/protocol-buffers/
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
@@ -449,7 +449,7 @@ bool Subprocess::Communicate(const Message& input, Message* output,
   }
 
   if (!output->ParseFromString(output_data)) {
-    *error = "Plugin output is unparseable.";
+    *error = "Plugin output is unparseable: " + CEscape(output_data);
     return false;
   }