Cleanup: Pass std::string as const reference if possible

chrome/common/icon_with_badge_image_source.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 CHROME_COMMON_ICON_WITH_BADGE_IMAGE_SOURCE_H_
 #define CHROME_COMMON_ICON_WITH_BADGE_IMAGE_SOURCE_H_
 
 #include <string>
 
 #include "third_party/skia/include/core/SkColor.h"
 #include "ui/gfx/image/canvas_image_source.h"
 #include "ui/gfx/image/image.h"
 
 namespace gfx {
 class Size;
 }
 
 // CanvasImageSource for creating extension icon with a badge.
 // TODO(devlin): This class and its buddy badge_util don't really belong in
 // chrome/common/.
 class IconWithBadgeImageSource : public gfx::CanvasImageSource {
  public:
   // The data representing a badge to be painted over the base image.
   struct Badge {
-    Badge(std::string text, SkColor text_color, SkColor background_color);
+    Badge(const std::string& text,
+          SkColor text_color,
+          SkColor background_color);
     ~Badge();
 
     std::string text;
     SkColor text_color;
     SkColor background_color;
 
    private:
     DISALLOW_COPY_AND_ASSIGN(Badge);
   };
 
@@ skipping 29 matching lines @@
   bool grayscale_;
 
   // Whether or not to paint a decoration over the base icon to indicate the
   // represented action wants to run.
   bool paint_decoration_;
 
   DISALLOW_COPY_AND_ASSIGN(IconWithBadgeImageSource);
 };
 
 #endif  // CHROME_COMMON_ICON_WITH_BADGE_IMAGE_SOURCE_H_