Makes ImageView do a bit more checking before assuming images equal

ui/views/controls/image_view.h

Index: ui/views/controls/image_view.h
diff --git a/ui/views/controls/image_view.h b/ui/views/controls/image_view.h
index 18c4ba13241ac01afe2d2604b3e361350dd32de5..b40cb83461f7c94a9cae9ab23ddd19a7fbfaa8fb 100644
--- a/ui/views/controls/image_view.h
+++ b/ui/views/controls/image_view.h
@@ -84,6 +84,11 @@ class VIEWS_EXPORT ImageView : public View {
   virtual bool HitTestRect(const gfx::Rect& rect) const OVERRIDE;
 
  private:
+  // Returns true if |img| is the same as the last image we painted. This is
+  // intended to be a quick check, not exhaustive. In other words it's possible
+  // for this to return false even though the images are in fact equal.
+  bool IsImageEqual(const gfx::ImageSkia& img) const;
+
   // Compute the image origin given the desired size and the receiver alignment
   // properties.
   gfx::Point ComputeImageOrigin(const gfx::Size& image_size) const;
@@ -109,6 +114,13 @@ class VIEWS_EXPORT ImageView : public View {
   // A flag controlling hit test handling for interactivity.
   bool interactive_;
 
+  // Scale last painted at.
+  float last_paint_scale_;
+
+  // Address of bytes we last painted. This is used only for comparison, so its
+  // safe to cache.
+  void* last_painted_bitmap_pixels_;
+
   DISALLOW_COPY_AND_ASSIGN(ImageView);
 };