Added method to synchronize command buffers within GpuControl.

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 df5489ca06f1d00eecf9297af4d3146be09eb41a..f8b9a6096beb10bcc3685ffb566d2c485beefb93 100644
--- a/components/mus/gles2/command_buffer_local.cc
+++ b/components/mus/gles2/command_buffer_local.cc
@@ -220,6 +220,10 @@ bool CommandBufferLocal::IsGpuChannelLost() {
   return false;
 }
 
+void CommandBufferLocal::SynchronizeCommandBuffer() {
+  // This is only relevant for out-of-process command buffers.
+}
+
 gpu::CommandBufferNamespace CommandBufferLocal::GetNamespaceID() const {
   return gpu::CommandBufferNamespace::MOJO_LOCAL;
 }