Open just folder menu on middle clicking chevron button.

chrome/browser/ui/cocoa/bookmarks/bookmark_bar_controller.h

 // 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.
 
 #ifndef CHROME_BROWSER_UI_COCOA_BOOKMARKS_BOOKMARK_BAR_CONTROLLER_H_
 #define CHROME_BROWSER_UI_COCOA_BOOKMARKS_BOOKMARK_BAR_CONTROLLER_H_
 
 #import <Cocoa/Cocoa.h>
 #include <map>
 
@@ skipping 371 matching lines @@
              parent:(const BookmarkNode*)oldParent index:(int)index;
 - (void)nodeFaviconLoaded:(BookmarkModel*)model
                      node:(const BookmarkNode*)node;
 - (void)nodeChildrenReordered:(BookmarkModel*)model
                          node:(const BookmarkNode*)node;
 @end
 
 // These APIs should only be used by unit tests (or used internally).
 @interface BookmarkBarController(InternalOrTestingAPI)
 - (void)openBookmarkFolder:(id)sender;
+- (void)openFolderForOffTheSideButton:(id)sender;
 - (BookmarkBarView*)buttonView;
 - (NSMutableArray*)buttons;
 - (NSButton*)offTheSideButton;
 - (NSButton*)appsPageShortcutButton;
 - (BOOL)offTheSideButtonIsHidden;
 - (BOOL)appsPageShortcutButtonIsHidden;
 - (BookmarkButton*)otherBookmarksButton;
 - (BookmarkBarFolderController*)folderController;
 - (id)folderTarget;
 - (int)displayedButtonCount;
@@ skipping 11 matching lines @@
 - (BookmarkButton*)buttonForDroppingOnAtPoint:(NSPoint)point;
 - (BOOL)isEventAnExitEvent:(NSEvent*)event;
 - (BOOL)shrinkOrHideView:(NSView*)view forMaxX:(CGFloat)maxViewX;
 - (void)unhighlightBookmark:(const BookmarkNode*)node;
 
 // The following are for testing purposes only and are not used internally.
 - (NSMenu *)menuForFolderNode:(const BookmarkNode*)node;
 @end
 
 #endif  // CHROME_BROWSER_UI_COCOA_BOOKMARKS_BOOKMARK_BAR_CONTROLLER_H_