Added a unique command buffer ID for command buffers.

ppapi/shared_impl/BUILD.gn

 # Copyright 2015 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.
 
 component("shared_impl") {
   output_name = "ppapi_shared"
 
   sources = [
     "array_var.cc",
     "array_var.h",
     "array_writer.cc",
     "array_writer.h",
     "callback_tracker.cc",
     "callback_tracker.h",
+    "command_buffer_id_pair.cc",
+    "command_buffer_id_pair.h",
     "compositor_layer_data.cc",
     "compositor_layer_data.h",
     "dictionary_var.cc",
     "dictionary_var.h",
     "file_growth.cc",
     "file_growth.h",
     "file_io_state_manager.cc",
     "file_io_state_manager.h",
     "file_path.cc",
     "file_path.h",
@@ skipping 176 matching lines @@
   deps = [
     "//base/test:test_support",
     "//ipc",
     "//ipc:test_support",
     "//ppapi/proxy",
     "//ppapi/shared_impl",
     "//testing/gmock",
     "//testing/gtest",
   ]
 }