views: refactor away PlatformStyle::BackgroundColorForMdButton

ui/gfx/color_utils.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_COLOR_UTILS_H_
 #define UI_GFX_COLOR_UTILS_H_
 
 #include "third_party/skia/include/core/SkColor.h"
 #include "ui/gfx/gfx_export.h"
 
@@ skipping 76 matching lines @@
 // bitmap are all the same brightness.
 GFX_EXPORT double CalculateBoringScore(const SkBitmap& bitmap);
 
 // Returns a blend of the supplied colors, ranging from |background| (for
 // |alpha| == 0) to |foreground| (for |alpha| == 255). The alpha channels of
 // the supplied colors are also taken into account, so the returned color may
 // be partially transparent.
 GFX_EXPORT SkColor AlphaBlend(SkColor foreground, SkColor background,
                               SkAlpha alpha);
 
+// Returns an AlphaBlend of the specified colors, using the alpha component of
+// the foreground color for the alpha and with the alpha of the foreground color

[Evan Stade, 2016/09/08 14:50:47]

I think the most intuitive way to explain this might be:

"Returns the color that results from painting |foreground| on top of
|background|."

[Elly Fong-Jones, 2016/09/08 16:06:12]

Done.

+// set to 1.0.
+GFX_EXPORT SkColor ImplicitAlphaBlend(SkColor foreground, SkColor background);
+
 // Returns true if the luma of |color| is closer to black than white.
 GFX_EXPORT bool IsDark(SkColor color);
 
 // Makes a dark color lighter or a light color darker by blending |color| with
 // white or black depending on its current luma.  |alpha| controls the amount of
 // white or black that will be alpha-blended into |color|.
 GFX_EXPORT SkColor BlendTowardOppositeLuma(SkColor color, SkAlpha alpha);
 
 // Given a foreground and background color, try to return a foreground color
 // that is "readable" over the background color by luma-inverting the foreground
@@ skipping 22 matching lines @@
 // light-on-dark color scheme.
 GFX_EXPORT bool IsInvertedColorScheme();
 
 // Derives a color for icons on a UI surface based on the text color on the same
 // surface.
 GFX_EXPORT SkColor DeriveDefaultIconColor(SkColor text_color);
 
 }  // namespace color_utils
 
 #endif  // UI_GFX_COLOR_UTILS_H_