Mac: give visual feedback for bookmark button drags.

chrome/browser/cocoa/bookmark_button.mm

 // Copyright (c) 2009 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 "base/logging.h"
 #import "base/scoped_nsobject.h"
 #import "chrome/browser/cocoa/bookmark_button.h"
 #import "chrome/browser/cocoa/bookmark_button_cell.h"
 #import "third_party/GTM/AppKit/GTMTheme.h"
 
 NSString* kBookmarkButtonDragType = @"ChromiumBookmarkButtonDragType";
 
 namespace {
 
 // Code taken from <http://codereview.chromium.org/180036/diff/3001/3004>.
 // TODO(viettrungluu): Do we want common, standard code for drag hysteresis?
 const CGFloat kWebDragStartHysteresisX = 5.0;
 const CGFloat kWebDragStartHysteresisY = 5.0;
 
 // The opacity of the bookmark button drag image.
-const CGFloat kDragImageOpacity = 0.8;
+const CGFloat kDragImageOpacity = 0.7;
 
 }
 
 @interface BookmarkButton(Private)
 
 // Make a drag image for the button.
 - (NSImage*)dragImage;
 
 @end  // @interface BookmarkButton(Private)
 
@@ skipping 130 matching lines @@
   [image drawAtPoint:NSMakePoint(0, 0)
             fromRect:NSMakeRect(0, 0, NSWidth(bounds), NSHeight(bounds))
            operation:NSCompositeSourceOver
             fraction:kDragImageOpacity];
 
   [dragImage unlockFocus];
   return dragImage;
 }
 
 @end  // @implementation BookmarkButton(Private)