[Mac] Fix "No drag (+) cursor displayed when dragging link over BMB"

chrome/browser/ui/cocoa/bookmarks/bookmark_bar_view.mm

 // Copyright (c) 2011 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.
 
 #import "chrome/browser/ui/cocoa/bookmarks/bookmark_bar_view.h"
 
 #include "chrome/browser/bookmarks/bookmark_pasteboard_helper_mac.h"
 #import "chrome/browser/ui/cocoa/bookmarks/bookmark_bar_controller.h"
 #import "chrome/browser/ui/cocoa/bookmarks/bookmark_button.h"
 #import "chrome/browser/ui/cocoa/bookmarks/bookmark_folder_target.h"
@@ skipping 137 matching lines @@
       // Need an update if the indicator wasn't previously shown or if it has
       // moved.
       if (!dropIndicatorShown_ || dropIndicatorPosition_ != x) {
         dropIndicatorShown_ = YES;
         dropIndicatorPosition_ = x;
         [self dropIndicatorChanged];
       }
     }
 
     [controller_ draggingEntered:info];  // allow hover-open to work.
-    return [info draggingSource] ? NSDragOperationMove : NSDragOperationCopy;
+    return [[info draggingSource] isKindOfClass: [BookmarkButton class]] ?
+        NSDragOperationMove : NSDragOperationCopy;
   }
   return NSDragOperationNone;
 }
 
 - (void)draggingExited:(id<NSDraggingInfo>)info {
   // Regardless of the type of dragging which ended, we need to get rid of the
   // drop indicator if one was shown.
   if (dropIndicatorShown_) {
     dropIndicatorShown_ = NO;
     [self dropIndicatorChanged];
@@ skipping 74 matching lines @@
 
 - (void)setController:(id)controller {
   controller_ = controller;
 }
 
 - (ViewID)viewID {
   return VIEW_ID_BOOKMARK_BAR;
 }
 
 @end  // @implementation BookmarkBarView