Fixed pass-by-value to pass-by-reference

ui/gfx/color_utils.h

 // Copyright (c) 2011 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_
 #pragma once
 
 #include "third_party/skia/include/core/SkColor.h"
 #include "ui/base/ui_export.h"
@@ skipping 40 matching lines @@
 // Determine if a color is near grey.
 bool IsColorCloseToGrey(int r, int g, int b);
 
 // Gets a color representing a bitmap. The definition of "representing" is the
 // average color in the bitmap. The color returned is modified to have the
 // specified alpha.
 SkColor GetAverageColorOfFavicon(SkBitmap* bitmap, SkAlpha alpha);
 
 // Builds a histogram based on the Y' of the Y'UV representation of
 // this image.
-UI_EXPORT void BuildLumaHistogram(SkBitmap* bitmap, int histogram[256]);
+UI_EXPORT void BuildLumaHistogram(const SkBitmap& bitmap, int histogram[256]);
 
 // 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.
 UI_EXPORT SkColor AlphaBlend(SkColor foreground, SkColor background,
                              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
 // color and then picking whichever foreground color has higher contrast against
 // the background color.
 //
 // NOTE: This won't do anything but waste time if the supplied foreground color
 // has a luma value close to the midpoint (0.5 in the HSL representation).
 UI_EXPORT SkColor GetReadableColor(SkColor foreground, SkColor background);
 
 // Gets a Windows system color as a SkColor
 UI_EXPORT SkColor GetSysSkColor(int which);
 
 }  // namespace color_utils
 
 #endif  // UI_GFX_COLOR_UTILS_H_