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..f7d8c6e7e697ae4d452a97c1650fa55fe4550068 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.
@@ -69,6 +70,11 @@ class UI_EXPORT ImageSkia {
 
   ~ImageSkia();
 
+  // Returns a deep copy of this ImageSkia which has its own storage with
+  // the same ImageSkiaRep instances. This can be safely passed to and
+  // manipulated by another thread.
+  ImageSkia DeepCopy() const;
+
   // Returns true if this object is backed by the same ImageSkiaStorage as
   // |other|. Will also return true if both images are isNull().
   bool BackedBySameObjectAs(const gfx::ImageSkia& other) const;
@@ -97,6 +103,11 @@ class UI_EXPORT ImageSkia {
   std::vector<ImageSkiaRep> GetRepresentations() const;
 #endif  // OS_MACOSX
 
+  // Make the image skia read only. Once it becomes read only,
+  // it can be safely accessed by any threads.
+  void SetReadOnly();
+  bool IsReadOnly() const;
+
   // Returns true if this is a null object.
   // TODO(pkotwicz): Merge this function into empty().
   bool isNull() const { return storage_ == NULL; }
@@ -120,6 +131,15 @@ 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 source 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.