Ensure that extension resources are loaded with the correct scaling applied on Windows.

ui/base/layout.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_BASE_LAYOUT_H_
 #define UI_BASE_LAYOUT_H_
 
 #include <vector>
 
 #include "build/build_config.h"
@@ skipping 40 matching lines @@
 // Use ScopedSetSupportedScaleFactors for unit tests as not to affect the
 // state of other tests.
 UI_BASE_EXPORT void SetSupportedScaleFactors(
     const std::vector<ScaleFactor>& scale_factors);
 
 // Returns a vector with the scale factors which are supported by this
 // platform, in ascending order.
 UI_BASE_EXPORT const std::vector<ScaleFactor>& GetSupportedScaleFactors();
 
 // Returns the float scale value for |scale_factor|.
+UI_BASE_EXPORT float GetImageScaleForScaleFactor(ScaleFactor scale_factor);
+
+// Returns the actual image scale to be used for the scale factor passed in.
+// For all platforms except Windows high dpi, this returns the value returned
+// by the GetImageScaleForScaleFactor function above.
+// For Windows with high dpi enabled it returns the dpi scale for the
+// display.
 UI_BASE_EXPORT float GetImageScale(ScaleFactor scale_factor);
 
 // Returns the supported ScaleFactor which most closely matches |scale|.
 // Converting from float to ScaleFactor is inefficient and should be done as
 // little as possible.
 // TODO(oshima): Make ScaleFactor a class and remove this.
 UI_BASE_EXPORT ScaleFactor GetSupportedScaleFactor(float image_scale);
 
 // Returns the ScaleFactor used by |view|.
 UI_BASE_EXPORT ScaleFactor GetScaleFactorForNativeView(gfx::NativeView view);
@@ skipping 19 matching lines @@
   std::vector<ui::ScaleFactor>* original_scale_factors_;
 
   DISALLOW_COPY_AND_ASSIGN(ScopedSetSupportedScaleFactors);
 };
 
 }  // namespace test
 
 }  // namespace ui
 
 #endif  // UI_BASE_LAYOUT_H_