Adds DevTools commands for forced viewport override.

content/renderer/gpu/render_widget_compositor.h

Index: content/renderer/gpu/render_widget_compositor.h
diff --git a/content/renderer/gpu/render_widget_compositor.h b/content/renderer/gpu/render_widget_compositor.h
index 5e875f9e69072b975dbcb02b0d59685d708ae77e..735a04dec1dd48b4b1245f1c896d9ff9b73b328b 100644
--- a/content/renderer/gpu/render_widget_compositor.h
+++ b/content/renderer/gpu/render_widget_compositor.h
@@ -109,6 +109,7 @@ class CONTENT_EXPORT RenderWidgetCompositor
   void detachCompositorAnimationTimeline(
       cc::AnimationTimeline* compositor_timeline) override;
   void setViewportSize(const blink::WebSize& device_viewport_size) override;
+  blink::WebSize getViewportSize() const override;
   virtual blink::WebFloatPoint adjustEventPointForPinchZoom(
       const blink::WebFloatPoint& point) const;
   void setDeviceScaleFactor(float device_scale) override;