chromeos: Gets OOPIF working for mus

The flow is:
1. browser requests WindowTreeClient from the RenderWidget of the
  frame to embed.
2. browser send a message to the parent RenderFrameProxy with the
   WindowTreeClient.
3. RenderFrameProxy forwards to RendererWindowTreeClient to create the
   child window and embed the WindowTreeClient in it.

BUG=758387
TEST=none

Cq-Include-Trybots: master.tryserver.chromium.linux:linux_site_isolation
Change-Id: I0296e802c0f754e463c65492f38ec5a68df30eba
Reviewed-on: https://chromium-review.googlesource.com/673066
Reviewed-by: Ken Buchanan <[email protected]>
Reviewed-by: Tom Sepez <[email protected]>
Reviewed-by: Sadrul Chowdhury <[email protected]>
Commit-Queue: Scott Violet <[email protected]>
Cr-Commit-Position: refs/heads/master@{#506819}
diff --git a/content/renderer/render_widget.h b/content/renderer/render_widget.h
index f10b9a0..bad68cf 100644
--- a/content/renderer/render_widget.h
+++ b/content/renderer/render_widget.h
@@ -274,7 +274,7 @@
   bool WillHandleGestureEvent(const blink::WebGestureEvent& event) override;
   bool WillHandleMouseEvent(const blink::WebMouseEvent& event) override;
 
-  // RenderWidgetScreenMetricsDelegate
+  // RenderWidgetScreenMetricsEmulatorDelegate
   void Redraw() override;
   void Resize(const ResizeParams& resize_params) override;
   void SetScreenMetricsEmulationParameters(