Add decode() functionality to image elements.

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 b0600bf7ec0e88731f885ec929eff87f90770493..4136f4b7c1f8b811daadbf7d9d0bb29f39c686ea 100644
--- a/content/renderer/gpu/render_widget_compositor.h
+++ b/content/renderer/gpu/render_widget_compositor.h
@@ -179,6 +179,8 @@ class CONTENT_EXPORT RenderWidgetCompositor
   // TODO(ianwen): Move this method to WebLayerTreeView and implement main
   // thread scrolling.
   virtual void setBottomControlsHeight(float height);
+  void requestDecode(sk_sp<SkImage> image,
+                     const base::Callback<void(bool)>& callback) override;
 
   // cc::LayerTreeHostClient implementation.
   void WillBeginMainFrame() override;