Add MGLEcho

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 769d81a2bfc618dcbc403933e3563824b0ece62b..cd51bd50ef3dbe5bad5f37e5a3e1a55b608d08f9 100644
--- a/mojo/gles2/command_buffer_client_impl.cc
+++ b/mojo/gles2/command_buffer_client_impl.cc
@@ -267,6 +267,10 @@ int32_t CommandBufferClientImpl::CreateGpuMemoryBufferImage(
   return -1;
 }
 
+void CommandBufferClientImpl::Echo(const base::Closure& callback) {
+  command_buffer_->Echo(callback);
+}
+
 uint32_t CommandBufferClientImpl::InsertSyncPoint() {
   command_buffer_->InsertSyncPoint(true);
   return sync_point_client_impl_->WaitForInsertSyncPoint();