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 a0b64ffa7688ddb4be15bc6f674d422f064bdfcd..4640b385f2c832b506bde1f00c5dfa082a7f57bb 100644
--- a/content/renderer/gpu/render_widget_compositor.h
+++ b/content/renderer/gpu/render_widget_compositor.h
@@ -182,6 +182,8 @@ 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;