Added GPU process "echo" IPC message.

content/renderer/gpu/renderer_gl_context.cc

Index: content/renderer/gpu/renderer_gl_context.cc
===================================================================
--- content/renderer/gpu/renderer_gl_context.cc	(revision 98655)
+++ content/renderer/gpu/renderer_gl_context.cc	(working copy)
@@ -192,10 +192,6 @@
   gles2_implementation_->DeleteTextures(1, &texture);
 }
 
-void RendererGLContext::SetSwapBuffersCallback(Callback0::Type* callback) {
-  swap_buffers_callback_.reset(callback);
-}
-
 void RendererGLContext::SetContextLostCallback(
     Callback1<ContextLostReason>::Type* callback) {
   context_lost_callback_.reset(callback);
@@ -229,9 +225,14 @@
     return false;
 
   gles2_implementation_->SwapBuffers();
+
   return true;
 }
 
+bool RendererGLContext::Echo(Task* task) {
+  return command_buffer_->Echo(task);
+}
+
 scoped_refptr<TransportTextureHost>
 RendererGLContext::CreateTransportTextureHost() {
   return channel_->transport_texture_service()->CreateTransportTextureHost(
@@ -368,9 +369,6 @@
     }
   }
 
-  command_buffer_->SetSwapBuffersCallback(
-      NewCallback(this, &RendererGLContext::OnSwapBuffers));
-
   command_buffer_->SetChannelErrorCallback(
       NewCallback(this, &RendererGLContext::OnContextLost));
 
@@ -445,11 +443,6 @@
   channel_ = NULL;
 }
 
-void RendererGLContext::OnSwapBuffers() {
-  if (swap_buffers_callback_.get())
-    swap_buffers_callback_->Run();
-}
-
 void RendererGLContext::OnContextLost() {
   if (context_lost_callback_.get()) {
     RendererGLContext::ContextLostReason reason = kUnknown;