Added GPU process "echo" IPC message.

content/renderer/pepper_platform_context_3d_impl.cc

Index: content/renderer/pepper_platform_context_3d_impl.cc
===================================================================
--- content/renderer/pepper_platform_context_3d_impl.cc	(revision 98655)
+++ content/renderer/pepper_platform_context_3d_impl.cc	(working copy)
@@ -111,11 +111,6 @@
   return true;
 }
 
-void PlatformContext3DImpl::SetSwapBuffersCallback(Callback0::Type* callback) {
-  DCHECK(command_buffer_);
-  command_buffer_->SetSwapBuffersCallback(callback);
-}
-
 unsigned PlatformContext3DImpl::GetBackingTextureId() {
   DCHECK(command_buffer_);
   return parent_texture_id_;
@@ -134,6 +129,10 @@
   context_lost_callback_.reset(callback);
 }
 
+bool PlatformContext3DImpl::Echo(Task* task) {
+  return command_buffer_->Echo(task);
+}
+
 void PlatformContext3DImpl::OnContextLost() {
   DCHECK(command_buffer_);