Load 2x resources on demand

ui/gfx/image/image_skia.h

Index: ui/gfx/image/image_skia.h
diff --git a/ui/gfx/image/image_skia.h b/ui/gfx/image/image_skia.h
index 24422d2f09a5559c1f28a53532925a83daa35130..5fac9e07ff501aee96413ce7c56291ec4302a3da 100644
--- a/ui/gfx/image/image_skia.h
+++ b/ui/gfx/image/image_skia.h
@@ -37,6 +37,7 @@ class UI_EXPORT ImageSkia {
 
   // Creates an instance that will use the |source| to get the image
   // for scale factors. |size| specifes the size of the image in DIP.
+  // ImageSkia owns |source|.
   ImageSkia(ImageSkiaSource* source, const gfx::Size& size);
 
   // Adds ref to passed in bitmap.
@@ -120,6 +121,15 @@ class UI_EXPORT ImageSkia {
   // when source is used.
   std::vector<gfx::ImageSkiaRep> image_reps() const;
 
+  // Delete the ImageSkiaSource if any. It will make GetRepresentation
+  // thread safe because it will no longer update the storage.
+  void DeleteSource();
+
+  // When the soruce is available, generates all ImageReps for
+  // supported scale factors. This method is defined as const as
+  // the state change in the storage is agnostic to the caller.
+  void EnsureRepsForSupportedScaleFactors() const;
+
  private:
   // Initialize ImageSkiaStorage with passed in parameters.
   // If the image rep's bitmap is empty, ImageStorage is set to NULL.