Squelch context menus on the OSX App List when both buttons are pressed.

ui/app_list/cocoa/apps_grid_view_item.mm

 // Copyright 2013 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 "ui/app_list/cocoa/apps_grid_view_item.h"
 
 #include "base/mac/foundation_util.h"
 #include "base/mac/mac_util.h"
 #include "base/mac/scoped_nsobject.h"
 #include "base/strings/sys_string_conversions.h"
@@ skipping 301 matching lines @@
 
 - (app_list::AppListItem*)model {
   return observerBridge_->model();
 }
 
 - (NSButton*)button {
   return [[self itemBackgroundView] button];
 }
 
 - (NSMenu*)contextMenu {
+  // Don't show the menu if button is already held down, e.g. with a left-click.
+  if ([[[self button] cell] isHighlighted])
+    return nil;
+
   [self setSelected:YES];
   return observerBridge_->GetContextMenu();
 }
 
 - (NSBitmapImageRep*)dragRepresentationForRestore:(BOOL)isRestore {
   NSButton* button = [self button];
   NSView* itemView = [self view];
 
   // The snapshot is never drawn as if it was selected. Also remove the cell
   // highlight on the button image, added when it was clicked.
@@ skipping 127 matching lines @@
 }
 
 // Workaround for http://crbug.com/324365: AppKit in Mavericks tries to call
 // - [NSButtonCell item] when inspecting accessibility. Without this, an
 // unrecognized selector exception is thrown inside AppKit, crashing Chrome.
 - (id)item {
   return nil;
 }
 
 @end