sync: add Google API Key to all ClientToServerMessages

sync/protocol/sync.proto

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
 // Sync protocol for communication between sync client and server.
 
 // Update proto_value_conversions{.h,.cc,_unittest.cc} if you change
 // any fields in this file.
 
 syntax = "proto2";
@@ skipping 481 matching lines @@
   optional bool sync_problem_detected = 8 [default = false];
 
   // Client side state information for debugging purpose.
   // This is only sent on the first getupdates of every sync cycle,
   // as an optimization to save bandwidth.
   optional DebugInfo debug_info = 10;
 
   // Per-client state for use by the server. Sent with every message sent to the
   // server.
   optional ChipBag bag_of_chips = 11;
+
+  // Google API key.
+  optional string api_key = 12;
 };
 
 message CommitResponse {
   enum ResponseType {
     SUCCESS = 1;
     CONFLICT = 2; // You're out of date; update and check your data
     // TODO(ncarter): What's the difference between RETRY and TRANSIENT_ERROR?
     RETRY = 3; // Someone has a conflicting, non-expired session open
     INVALID_MESSAGE = 4; // What the client sent was invalid, and trying again
                          // won't help.
@@ skipping 173 matching lines @@
     // is absent then the whole client (all datatypes) is throttled.
     repeated int32 error_data_type_ids = 5;
   }
   optional Error error = 13;
 
   // The new per-client state for this client. If set, should be persisted and
   // sent with any subsequent ClientToServerMessages.
   optional ChipBag new_bag_of_chips = 14;
 };