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 178de61c237bf73d40c46234a9ea8febe79af365..99b801846aeb6c13bcb94da7088b0d4167ab9c6a 100644
--- a/components/mus/gles2/command_buffer_local.cc
+++ b/components/mus/gles2/command_buffer_local.cc
@@ -228,6 +228,10 @@ uint64_t CommandBufferLocal::GetCommandBufferID() const {
   return command_buffer_id_;
 }
 
+int32_t CommandBufferLocal::GetExtraCommandBufferData() const {
+  return 0;
+}
+
 uint64_t CommandBufferLocal::GenerateFenceSyncRelease() {
   return next_fence_sync_release_++;
 }