Added method to synchronize command buffers within GpuControl.

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 b749147fc6f2a2ea52c167ef468ab869bb67f03c..5f30b5afea1757cc2683aba978ad5156e2517154 100644
--- a/mojo/gles2/command_buffer_client_impl.cc
+++ b/mojo/gles2/command_buffer_client_impl.cc
@@ -350,6 +350,10 @@ bool CommandBufferClientImpl::IsGpuChannelLost() {
   return false;
 }
 
+void CommandBufferClientImpl::SynchronizeCommandBuffer() {
+  // This is only relevant for out-of-process command buffers.
+}
+
 gpu::CommandBufferNamespace CommandBufferClientImpl::GetNamespaceID() const {
   return gpu::CommandBufferNamespace::MOJO;
 }