[Mac] Set tooltip for the app menu button

chrome/browser/ui/cocoa/toolbar/app_toolbar_button.mm

 // Copyright 2016 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/toolbar/app_toolbar_button.h"
 
 #include "base/macros.h"
 #include "chrome/app/vector_icons/vector_icons.h"
 #import "chrome/browser/ui/cocoa/themed_window.h"
 #import "chrome/browser/ui/cocoa/view_id_util.h"
+#include "chrome/grit/chromium_strings.h"
+#include "ui/base/l10n/l10n_util_mac.h"
 #include "ui/base/material_design/material_design_controller.h"
 #include "ui/base/theme_provider.h"
 #include "ui/gfx/color_palette.h"
 
 @interface AppToolbarButton ()
 - (void)commonInit;
 @end
 
 @implementation AppToolbarButton
 
 - (instancetype)initWithFrame:(NSRect)frame {
   if ((self = [super initWithFrame:frame])) {
     [self commonInit];
   }
   return self;
 }
 
 - (void)awakeFromNib {
   [self commonInit];
 }
 
 - (void)commonInit {
   view_id_util::SetID(self, VIEW_ID_APP_MENU);
   severity_ = AppMenuIconController::Severity::NONE;
   type_ = AppMenuIconController::IconType::NONE;
+  [self setToolTip:l10n_util::GetNSString(IDS_APPMENU_TOOLTIP)];
 }
 
 - (const gfx::VectorIcon*)vectorIcon {
   switch (type_) {
     case AppMenuIconController::IconType::NONE:
       DCHECK_EQ(severity_, AppMenuIconController::Severity::NONE);
       return &kBrowserToolsIcon;
     case AppMenuIconController::IconType::UPGRADE_NOTIFICATION:
       return &kBrowserToolsUpdateIcon;
     case AppMenuIconController::IconType::GLOBAL_ERROR:
@@ skipping 36 matching lines @@
       shouldAnimate:(BOOL)shouldAnimate {
   if (severity != severity_ || type != type_) {
     severity_ = severity;
     type_ = type;
     // Update the button state images with the new severity color or icon type.
     [self resetButtonStateImages];
   }
 }
 
 @end