Implement dragging icon for dragging bookmarks in views/gtk.

app/gfx/canvas.cc

 // Copyright (c) 2006-2008 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.
 
 #include "app/gfx/canvas.h"
 
 #include <limits>
 
 #include "app/gfx/font.h"
 #include "app/l10n_util.h"
@@ skipping 230 matching lines @@
   // CreateBitmapShader returns a Shader with a reference count of one, we
   // need to unref after paint takes ownership of the shader.
   shader->unref();
   save();
   translate(SkIntToScalar(dest_x - src_x), SkIntToScalar(dest_y - src_y));
   ClipRectInt(src_x, src_y, w, h);
   drawPaint(paint);
   restore();
 }
 
-SkBitmap Canvas::ExtractBitmap() {
+SkBitmap Canvas::ExtractBitmap() const {
   const SkBitmap& device_bitmap = getDevice()->accessBitmap(false);
 
   // Make a bitmap to return, and a canvas to draw into it. We don't just want
   // to call extractSubset or the copy constuctor, since we want an actual copy
   // of the bitmap.
   SkBitmap result;
   device_bitmap.copyTo(&result, SkBitmap::kARGB_8888_Config);
   return result;
 }
 
 }  // namespace gfx