Added a unique command buffer ID for command buffers.

ppapi/shared_impl/command_buffer_id_pair.cc

+// 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.
+
+#include "ppapi/shared_impl/command_buffer_id_pair.h"
+
+namespace ppapi {
+
+CommandBufferIDPair::CommandBufferIDPair()
+    : namespace_id(gpu::kCommandBufferNamespace_Invalid),
+      command_buffer_id(0) {
+}
+
+CommandBufferIDPair::~CommandBufferIDPair() {}
+
+} // namespace ppapi