[Mac] Adjust omnibox decoration dragging to keep image under mouse.

chrome/browser/cocoa/location_bar/location_bar_decoration.h

 // Copyright (c) 2010 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_BROWSER_COCOA_LOCATION_BAR_LOCATION_BAR_DECORATION_H_
 #define CHROME_BROWSER_COCOA_LOCATION_BAR_LOCATION_BAR_DECORATION_H_
 
 #import <Cocoa/Cocoa.h>
 
 #import "base/basictypes.h"
@@ skipping 41 matching lines @@
   // I-beam cursor.  Decorations which do accept mouse events will get
   // an arrow cursor when the mouse is over them.
   virtual bool AcceptsMousePress() { return false; }
 
   // Determine if the item can act as a drag source.
   virtual bool IsDraggable() { return false; }
 
   // The image to drag.
   virtual NSImage* GetDragImage() { return nil; }
 
+  // Return the place within the decoration's frame where the
+  // |GetDragImage()| comes from.  This is used to make sure the image
+  // appears correctly under the mouse while dragging.  |frame|
+  // matches the frame passed to |DrawInFrame()|.
+  virtual NSRect GetDragImageFrame(NSRect frame) { return NSZeroRect; }
+
   // The pasteboard to drag.
   virtual NSPasteboard* GetDragPasteboard() { return nil; }
 
   // Called on mouse down.  Return |false| to indicate that the press
   // was not processed and should be handled by the cell.
   virtual bool OnMousePressed(NSRect frame) { return false; }
 
   // Called to get the right-click menu, return |nil| for no menu.
   virtual NSMenu* GetMenu() { return nil; }
 
   // Width returned by |GetWidthForSpace()| when the item should be
   // omitted for this width;
   static const CGFloat kOmittedWidth;
 
  private:
   bool visible_;
 
   DISALLOW_COPY_AND_ASSIGN(LocationBarDecoration);
 };
 
 #endif  // CHROME_BROWSER_COCOA_LOCATION_BAR_LOCATION_BAR_DECORATION_H_