The extension icon on the far right is invisible when about to dragging.

chrome/browser/ui/cocoa/extensions/browser_actions_controller.mm

 // Copyright (c) 2012 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/extensions/browser_actions_controller.h"
 
 #include <cmath>
 #include <string>
 
 #include "base/strings/sys_string_conversions.h"
@@ skipping 619 matching lines @@
 
 - (void)containerFrameChanged:(NSNotification*)notification {
   [self updateButtonOpacity];
   [[containerView_ window] invalidateCursorRectsForView:containerView_];
   [self updateChevronPositionInFrame:[containerView_ frame]];
 }
 
 - (void)containerDragStart:(NSNotification*)notification {
   [self setChevronHidden:YES inFrame:[containerView_ frame] animate:YES];
   while([hiddenButtons_ count] > 0) {
-    [containerView_ addSubview:[hiddenButtons_ objectAtIndex:0]];
+    BrowserActionButton* button = [hiddenButtons_ objectAtIndex:0];
+    [button setAlphaValue:1.0];
+    [containerView_ addSubview:button];
     [hiddenButtons_ removeObjectAtIndex:0];
   }
 }
 
 - (void)containerDragging:(NSNotification*)notification {
   [[NSNotificationCenter defaultCenter]
       postNotificationName:kBrowserActionGrippyDraggingNotification
                     object:self];
 }
 
@@ skipping 205 matching lines @@
   const extensions::ExtensionList& toolbar_items =
       toolbarModel_->toolbar_items();
   if (index < toolbar_items.size()) {
     const Extension* extension = toolbar_items[index].get();
     return [buttons_ objectForKey:base::SysUTF8ToNSString(extension->id())];
   }
   return nil;
 }
 
 @end