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

mojo/gles2/command_buffer_client_impl.cc

Index: mojo/gles2/command_buffer_client_impl.cc
diff --git a/mojo/gles2/command_buffer_client_impl.cc b/mojo/gles2/command_buffer_client_impl.cc
index 6e3e2a64a0d115532769e569ca59c477a3907fac..79f238ad25a0a8b5c836a5363e801f204646ce34 100644
--- a/mojo/gles2/command_buffer_client_impl.cc
+++ b/mojo/gles2/command_buffer_client_impl.cc
@@ -413,6 +413,10 @@ uint64_t CommandBufferClientImpl::GetCommandBufferID() const {
   return sync_client_impl_->GetCommandBufferID();
 }
 
+int32_t CommandBufferClientImpl::GetExtraCommandBufferData() const {
+  return 0;
+}
+
 uint64_t CommandBufferClientImpl::GenerateFenceSyncRelease() {
   return next_fence_sync_release_++;
 }