Added GPU process "echo" IPC message.

content/renderer/gpu/webgraphicscontext3d_command_buffer_impl.cc

Index: content/renderer/gpu/webgraphicscontext3d_command_buffer_impl.cc
===================================================================
--- content/renderer/gpu/webgraphicscontext3d_command_buffer_impl.cc	(revision 98655)
+++ content/renderer/gpu/webgraphicscontext3d_command_buffer_impl.cc	(working copy)
@@ -49,7 +49,8 @@
       swapbuffers_complete_callback_(0),
       cached_width_(0),
       cached_height_(0),
-      bound_fbo_(0) {
+      bound_fbo_(0),
+      method_factory_(ALLOW_THIS_IN_INITIALIZER_LIST(this)) {
 }
 
 WebGraphicsContext3DCommandBufferImpl::
@@ -137,11 +138,6 @@
         preferred_extensions,
         attribs,
         active_url);
-    if (context_) {
-      context_->SetSwapBuffersCallback(
-          NewCallback(this,
-              &WebGraphicsContext3DCommandBufferImpl::OnSwapBuffersComplete));
-    }
   } else {
     context_ = RendererGLContext::CreateOffscreenContext(
         host,
@@ -230,6 +226,8 @@
     renderview->OnViewContextSwapBuffersPosted();
 #endif
   context_->SwapBuffers();
+  context_->Echo(method_factory_.NewRunnableMethod(
+      &WebGraphicsContext3DCommandBufferImpl::OnSwapBuffersComplete));
 #if defined(OS_MACOSX)
   // It appears that making the compositor's on-screen context current on
   // other platforms implies this flush. TODO(kbr): this means that the