Plumb ViewportMetrics change notifications around the world and back.

sky/viewer/document_view.h

Index: sky/viewer/document_view.h
diff --git a/sky/viewer/document_view.h b/sky/viewer/document_view.h
index 58e526d3040aeb67be53deb1194578357b40d80f..3c57354cfa5ca134d6861c5443a0a855850eab2e 100644
--- a/sky/viewer/document_view.h
+++ b/sky/viewer/document_view.h
@@ -112,6 +112,10 @@ class DocumentView : public blink::ServiceProvider,
   void OnViewBoundsChanged(mojo::View* view,
                            const mojo::Rect& old_bounds,
                            const mojo::Rect& new_bounds) override;
+  void OnViewViewportMetricsChanged(
+      mojo::View* view,
+      const mojo::ViewportMetrics& old_metrics,
+      const mojo::ViewportMetrics& new_metrics) override;
   void OnViewFocusChanged(mojo::View* gained_focus,
                           mojo::View* lost_focus) override;
   void OnViewDestroyed(mojo::View* view) override;
@@ -121,6 +125,8 @@ class DocumentView : public blink::ServiceProvider,
   float GetDevicePixelRatio() const;
   scoped_ptr<Rasterizer> CreateRasterizer();
 
+  void UpdateRootSizeAndViewportMetrics(const mojo::Rect& new_bounds);
+
   mojo::URLResponsePtr response_;
   mojo::ServiceProviderImpl exported_services_;
   mojo::ServiceProviderPtr imported_services_;