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..fbe84853e6e14feb7169e5ad81c6085d5a027fd6 100644
--- a/ui/gfx/image/image_skia.h
+++ b/ui/gfx/image/image_skia.h
@@ -75,6 +75,11 @@ class GFX_EXPORT ImageSkia {
   // Returns the maximum scale supported by this platform.
   static float GetMaxSupportedScale();
 
+  // Maps to the closest supported scale. Returns an exact match, a smaller
+  // scale within 0.2 units, the nearest larger scale, or the min/max
+  // supported scale.
+  static float MapToSupportedScale(float scale);
+
   // Creates an image from the passed in bitmap.
   // DIP width and height are based on scale factor of 1x.
   // Adds ref to passed in bitmap.