Allow out-of-process iframes to render to compositing surfaces.

content/browser/frame_host/render_widget_host_view_guest.cc

Index: content/browser/frame_host/render_widget_host_view_guest.cc
diff --git a/content/browser/frame_host/render_widget_host_view_guest.cc b/content/browser/frame_host/render_widget_host_view_guest.cc
index 3a0239bb19751741c50c9cad4cdc12f53341d454..c1a3419de0d08501c36c7fd81414c990d32ee03a 100644
--- a/content/browser/frame_host/render_widget_host_view_guest.cc
+++ b/content/browser/frame_host/render_widget_host_view_guest.cc
@@ -389,6 +389,11 @@ void RenderWidgetHostViewGuest::GetScreenInfo(blink::WebScreenInfo* results) {
     embedder_view->GetScreenInfo(results);
 }
 
+uint32_t RenderWidgetHostViewGuest::GetSurfaceIdNamespace() {
+  // Compositing surfaces not supported.

[ncarter (slow), 2015/05/28 22:32:52]

Is this a job for NOTIMPLEMENTED()? Or will we not eventually have to make this
work?

[kenrb, 2015/05/29 19:29:36]

We will want to make it work later, but in the meantime this method will get
called sometimes anyway. The placeholder '0' ends up getting passed to the
LayerTreeHost in the renderer process and never used (because no surfaces will
be created).

+  return 0;
+}
+
 #if defined(OS_MACOSX)
 void RenderWidgetHostViewGuest::SetActive(bool active) {
   platform_view_->SetActive(active);