Make some updates to BM bar for MD.

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 "base/basictypes.h"
 #include "third_party/skia/include/core/SkColor.h"
 #include "ui/gfx/gfx_export.h"
 
 class SkBitmap;
 
 namespace color_utils {
 
 // Represents an HSL color.
 struct HSL {
   double h;
   double s;
   double l;
 };
 
+// The minimum contrast between text and background that is still readable.
+// This value is taken from w3c accessibility guidelines.
+const double kMinimumReadableContrastRatio = 4.5f;
+
+// Determines the contrast ratio of two colors.
+GFX_EXPORT double GetContrastRatio(SkColor color_a, SkColor color_b);
+
 GFX_EXPORT unsigned char GetLuminanceForColor(SkColor color);
 
 // Calculated according to http://www.w3.org/TR/WCAG20/#relativeluminancedef
 GFX_EXPORT double RelativeLuminance(SkColor color);
 
 // Note: these transformations assume sRGB as the source color space
 GFX_EXPORT void SkColorToHSL(SkColor c, HSL* hsl);
 GFX_EXPORT SkColor HSLToSkColor(const HSL& hsl, SkAlpha alpha);
 
 // Determines whether the given |hsl| falls within the given range for each
@@ skipping 75 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_