Make echo message per-command-buffer

content/common/gpu/gpu_command_buffer_stub.cc

Index: content/common/gpu/gpu_command_buffer_stub.cc
diff --git a/content/common/gpu/gpu_command_buffer_stub.cc b/content/common/gpu/gpu_command_buffer_stub.cc
index 09187aa502c4f5d5ebdd7fd727a9d17437a7727b..9222a69b2f4188cc5972081678370b6cd405b526 100644
--- a/content/common/gpu/gpu_command_buffer_stub.cc
+++ b/content/common/gpu/gpu_command_buffer_stub.cc
@@ -103,6 +103,7 @@ bool GpuCommandBufferStub::OnMessageReceived(const IPC::Message& message) {
                                     OnSetSharedStateBuffer);
     IPC_MESSAGE_HANDLER_DELAY_REPLY(GpuCommandBufferMsg_SetParent,
                                     OnSetParent);
+    IPC_MESSAGE_HANDLER(GpuCommandBufferMsg_Echo, OnEcho);
     IPC_MESSAGE_HANDLER_DELAY_REPLY(GpuCommandBufferMsg_GetState, OnGetState);
     IPC_MESSAGE_HANDLER_DELAY_REPLY(GpuCommandBufferMsg_GetStateFast,
                                     OnGetStateFast);
@@ -141,6 +142,11 @@ bool GpuCommandBufferStub::HasMoreWork() {
   return scheduler_.get() && scheduler_->HasMoreWork();
 }
 
+void GpuCommandBufferStub::OnEcho(const IPC::Message& message) {
+  TRACE_EVENT0("gpu", "GpuCommandBufferStub::OnEcho");
+  Send(new IPC::Message(message));
+}
+
 void GpuCommandBufferStub::Destroy() {
   // The scheduler has raw references to the decoder and the command buffer so
   // destroy it before those.