Added a unique command buffer ID for command buffers.

content/common/gpu/gpu_command_buffer_stub.h

Index: content/common/gpu/gpu_command_buffer_stub.h
diff --git a/content/common/gpu/gpu_command_buffer_stub.h b/content/common/gpu/gpu_command_buffer_stub.h
index 3e26fcb116e66f97444617716b8bb8b74c81ddfe..971d1da795172a5dcc477f819a54731d0d84c04d 100644
--- a/content/common/gpu/gpu_command_buffer_stub.h
+++ b/content/common/gpu/gpu_command_buffer_stub.h
@@ -117,6 +117,9 @@ class GpuCommandBufferStub
   gpu::GpuScheduler* scheduler() const { return scheduler_.get(); }
   GpuChannel* channel() const { return channel_; }
 
+  // Unique command buffer ID for this command buffer stub.
+  uint64_t command_buffer_id() const { return command_buffer_id_; }
+
   // Identifies the target surface.
   int32 surface_id() const { return surface_id_; }
 
@@ -262,6 +265,7 @@ class GpuCommandBufferStub
   std::vector<int32> requested_attribs_;
   gfx::GpuPreference gpu_preference_;
   bool use_virtualized_gl_context_;
+  const uint64_t command_buffer_id_;
   const int32 stream_id_;
   const int32 route_id_;
   const int32 surface_id_;