arc: Support non-standard display scale factors.

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 db7447d986c08a497371523456e372544a5d21be..92fabe50ac1351c3a144358bb3061fa5f1bbd711 100644
--- a/ui/gfx/image/image_skia.h
+++ b/ui/gfx/image/image_skia.h
@@ -150,6 +150,10 @@ class GFX_EXPORT ImageSkia {
   // the state change in the storage is agnostic to the caller.
   void EnsureRepsForSupportedScales() const;
 
+  // Clears cached representations for non-supported scale factors that are
+  // based on |scale|.
+  void RemoveUnsupportedRepresentationsForScale(float scale);
+
  private:
   friend class test::TestOnThread;
   FRIEND_TEST_ALL_PREFIXES(ImageSkiaTest, EmptyOnThreadTest);