Added an extra sync token field for extra command buffer identification.

ppapi/proxy/ppapi_command_buffer_proxy.h

Index: ppapi/proxy/ppapi_command_buffer_proxy.h
diff --git a/ppapi/proxy/ppapi_command_buffer_proxy.h b/ppapi/proxy/ppapi_command_buffer_proxy.h
index 072d91d29811d3815523b3e54259dafcd7a08aaf..e30ca435b585c8464ae427c64467e632750f5e82 100644
--- a/ppapi/proxy/ppapi_command_buffer_proxy.h
+++ b/ppapi/proxy/ppapi_command_buffer_proxy.h
@@ -76,6 +76,7 @@ class PPAPI_PROXY_EXPORT PpapiCommandBufferProxy : public gpu::CommandBuffer,
   void SignalSyncToken(const gpu::SyncToken& sync_token,
                        const base::Closure& callback) override;
   bool CanWaitUnverifiedSyncToken(const gpu::SyncToken* sync_token) override;
+  uint32_t GetExtraCommandBufferData() const override;
 
  private:
   bool Send(IPC::Message* msg);