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

components/mus/gles2/command_buffer_local.cc

Index: components/mus/gles2/command_buffer_local.cc
diff --git a/components/mus/gles2/command_buffer_local.cc b/components/mus/gles2/command_buffer_local.cc
index d84c53ace1a7761a8e9b0a9742419a0b4618de73..60c8c67a074790ce7dbd2ca1ebb7dfc5e3c515de 100644
--- a/components/mus/gles2/command_buffer_local.cc
+++ b/components/mus/gles2/command_buffer_local.cc
@@ -233,6 +233,10 @@ uint64_t CommandBufferLocal::GetCommandBufferID() const {
   return command_buffer_id_;
 }
 
+uint32_t CommandBufferLocal::GetExtraCommandBufferData() const {
+  return 0;
+}
+
 uint64_t CommandBufferLocal::GenerateFenceSyncRelease() {
   return next_fence_sync_release_++;
 }