Give the main frame a RenderWidget.

content/browser/renderer_host/render_view_host_factory.cc

Index: content/browser/renderer_host/render_view_host_factory.cc
diff --git a/content/browser/renderer_host/render_view_host_factory.cc b/content/browser/renderer_host/render_view_host_factory.cc
index bfa5c98fff9dfe665189c61fba585c48a5dc65ea..42c20caa1d37cbc230a3d8372ab34b4b7b833536 100644
--- a/content/browser/renderer_host/render_view_host_factory.cc
+++ b/content/browser/renderer_host/render_view_host_factory.cc
@@ -22,6 +22,9 @@ RenderViewHost* RenderViewHostFactory::Create(
     int32 main_frame_routing_id,
     bool swapped_out,
     bool hidden) {
+  // TODO(dcheng): Once the main frame's RenderWidgetHost is used for painting,
+  // the surface creation/lookup here can be removed and the values hardcoded to
+  // 0. https://crbug.com/526958
   int32 surface_id;
   // RenderViewHost creation can be either browser-driven (by the user opening a
   // new tab) or renderer-driven (by script calling window.open, etc).