Refactor ShadowImageSource into ui/gfx/skia_util for better reuse

ui/gfx/image/image_skia_operations.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_IMAGE_IMAGE_SKIA_OPERATIONS_H_
 #define UI_GFX_IMAGE_IMAGE_SKIA_OPERATIONS_H_
 
 #include "skia/ext/image_operations.h"
 #include "ui/gfx/color_utils.h"
 #include "ui/gfx/gfx_export.h"
@@ skipping 69 matching lines @@
 
   // Creates an image by resizing |source| to given |target_dip_size|.
   static ImageSkia CreateResizedImage(const ImageSkia& source,
                                       skia::ImageOperations::ResizeMethod methd,
                                       const Size& target_dip_size);
 
   // Creates an image with drop shadow defined in |shadows| for |source|.
   static ImageSkia CreateImageWithDropShadow(const ImageSkia& source,
                                              const ShadowValues& shadows);
 
+  // Creates an image that is 1dp wide, suitable for tiling horizontally to
+  // create a drop shadow effect. The purpose of tiling a static image is to
+  // avoid repeatedly asking Skia to draw a shadow.
+  static gfx::ImageSkia CreateHorizontalShadow(
+      const std::vector<ShadowValue>& shadows,
+      bool fades_down);
+
   // Creates an image which is a rotation of the |source|. |rotation| is the
   // amount of clockwise rotation in degrees.
   static ImageSkia CreateRotatedImage(
       const ImageSkia& source,
       SkBitmapOperations::RotationAmount rotation);
 
   // Creates an icon by painting the second icon as a badge to the first one.
   // The second icon is in the right corner of the first icon. If the icon
   // is valid and the badge is not, the icon will be returned.
   static ImageSkia CreateIconWithBadge(const ImageSkia& icon,
                                        const ImageSkia& badge);
 
  private:
   ImageSkiaOperations();  // Class for scoping only.
 };
 
 }  // namespace gfx
 
 #endif  // UI_GFX_IMAGE_IMAGE_SKIA_OPERATIONS_H_