arc: Support non-standard display scale factors.

ui/gfx/image/image_skia.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_GFX_IMAGE_IMAGE_SKIA_H_
 #define UI_GFX_IMAGE_IMAGE_SKIA_H_
 
 #include <memory>
 #include <vector>
 
@@ skipping 57 matching lines @@
   // Changes the value of GetSupportedScales() to |scales|.
   static void SetSupportedScales(const std::vector<float>& scales);
 
   // Returns a vector with the scale factors which are supported by this
   // platform, in ascending order.
   static const std::vector<float>& GetSupportedScales();
 
   // Returns the maximum scale supported by this platform.
   static float GetMaxSupportedScale();
 
+  // Maps to closest supported scale.

[msw, 2017/05/24 20:27:59]

nit: "Maps |scale| to the closest supported scale."
Should it say something about preferring higher or lower scales?

[khmel, 2017/05/24 21:32:37]

Done.

+  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.
   // WARNING: The resulting image will be pixelated when painted on a high
   // density display.
   static ImageSkia CreateFrom1xBitmap(const SkBitmap& bitmap);
 
   // Returns a deep copy of this ImageSkia which has its own storage with
   // the ImageSkiaRep instances that this ImageSkia currently has.
   // This can be safely passed to and manipulated by another thread.
@@ skipping 82 matching lines @@
   // so that other thread can access the storage.
   void DetachStorageFromThread();
 
   // A refptr so that ImageRepSkia can be copied cheaply.
   scoped_refptr<internal::ImageSkiaStorage> storage_;
 };
 
 }  // namespace gfx
 
 #endif  // UI_GFX_IMAGE_IMAGE_SKIA_H_