Pass the ImageSkia by pointer instead of by reference, which will create shallow copy.

ui/gfx/image/image_skia.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_H_
 #define UI_GFX_IMAGE_IMAGE_SKIA_H_
 
 #include <vector>
 
 #include "base/basictypes.h"
 #include "base/gtest_prod_util.h"
 #include "base/memory/ref_counted.h"
+#include "base/memory/scoped_ptr.h"
 #include "ui/base/ui_export.h"
 #include "ui/gfx/image/image_skia_rep.h"
 
 namespace gfx {
 class ImageSkiaSource;
 class Size;
 
 namespace internal {
 class ImageSkiaStorage;
 }  // namespace internal
@@ skipping 48 matching lines @@
 
   ~ImageSkia();
 
   // Returns a deep copy of this ImageSkia which has its own storage with
   // the ImageSkiaRep instances that this ImageSkia currently has.
   // This can be safely passed to and manipulated by another thread.
   // Note that this does NOT generate ImageSkiaReps from its source.
   // If you want to create a deep copy with ImageSkiaReps for supported
   // scale factors, you need to explicitly call
   // |EnsureRepsForSupportedScaleFactors()| first.
-  ImageSkia DeepCopy() const;
+  scoped_ptr<ImageSkia> DeepCopy() const;
 
   // Returns true if this object is backed by the same ImageSkiaStorage as
   // |other|. Will also return true if both images are isNull().
   bool BackedBySameObjectAs(const gfx::ImageSkia& other) const;
 
   // Adds |image_rep| to the image reps contained by this object.
   void AddRepresentation(const gfx::ImageSkiaRep& image_rep);
 
   // Removes the image rep of |scale_factor| if present.
   void RemoveRepresentation(ui::ScaleFactor scale_factor);
@@ skipping 69 matching lines @@
   // so that other thread can access the storage.
   void DetachStorageFromThread();
 
   // A refptr so that ImageRepSkia can be copied cheaply.
   scoped_refptr<internal::ImageSkiaStorage> storage_;
 };
 
 }  // namespace gfx
 
 #endif  // UI_GFX_IMAGE_IMAGE_SKIA_H_