Implement dragging icon for dragging bookmarks in views/gtk.

app/gfx/canvas.h

 // 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.
 
 #ifndef APP_GFX_CANVAS_H_
 #define APP_GFX_CANVAS_H_
 
 #if defined(OS_WIN)
 #include <windows.h>
 #endif
@@ skipping 162 matching lines @@
 
   // Draws a dotted gray rectangle used for focus purposes.
   void DrawFocusRect(int x, int y, int width, int height);
 
   // Tiles the image in the specified region.
   void TileImageInt(const SkBitmap& bitmap, int x, int y, int w, int h);
   void TileImageInt(const SkBitmap& bitmap, int src_x, int src_y,
                     int dest_x, int dest_y, int w, int h);
 
   // Extracts a bitmap from the contents of this canvas.
-  SkBitmap ExtractBitmap();
+  SkBitmap ExtractBitmap() const;
 
 #if defined(OS_LINUX)
   // Applies current matrix on the canvas to the cairo context. This should be
   // invoked anytime you plan on drawing directly to the cairo context. Be
   // sure and set the matrix back to the identity when done.
   void ApplySkiaMatrixToCairoContext(cairo_t* cr);
 
   // Draw the pixbuf in its natural size at (x, y).
   void DrawGdkPixbuf(GdkPixbuf* pixbuf, int x, int y);
 #endif
@@ skipping 14 matching lines @@
                      const SkColor& color, int x, int y, int w, int h,
                      int flags);
 #endif
 
   DISALLOW_COPY_AND_ASSIGN(Canvas);
 };
 
 }  // namespace gfx;
 
 #endif  // APP_GFX_CANVAS_H_