Turn off the tip for the sytem tray menu and the app list (ChromeOS).

ash/system/tray/system_tray.cc

 // 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.
 
 #include "ash/system/tray/system_tray.h"
 
 #include "ash/ash_switches.h"
 #include "ash/shelf/shelf_layout_manager.h"
 #include "ash/shell.h"
 #include "ash/shell/panel_window.h"
@@ skipping 71 matching lines @@
   // Initializes the bubble view and creates |bubble_wrapper_|.
   void InitView(TrayBackgroundView* tray,
                 views::View* anchor,
                 TrayBubbleView::InitParams* init_params) {
     DCHECK(anchor);
     user::LoginStatus login_status =
         Shell::GetInstance()->system_tray_delegate()->GetUserLoginStatus();
     bubble_->InitView(anchor, login_status, init_params);
     bubble_wrapper_.reset(
         new internal::TrayBubbleWrapper(tray, bubble_->bubble_view()));
+    if (ash::switches::UseAlternateShelfLayout()) {
+      // The system bubble should not have an arrow.
+      bubble_->bubble_view()->SetArrowPaintType(
+          views::BubbleBorder::PAINT_NONE);
+    }

[simonhong_, 2013/06/15 15:21:07]

This code is actually changing PAINT_NORMAL to PAINT_NONE after
creating(showing) the bubble. (tray bubble is created at the ctor of
TrayBubbleWrapper).
I think setting the arrow before the bubble_view_->InitializeAndShowBubble() is
better than here.

   }
 
   // Convenience accessors:
   SystemTrayBubble* bubble() const { return bubble_.get(); }
   SystemTrayBubble::BubbleType bubble_type() const {
     return bubble_->bubble_type();
   }
   TrayBubbleView* bubble_view() const { return bubble_->bubble_view(); }
 
  private:
@@ skipping 401 matching lines @@
 
 void SystemTray::AnchorUpdated() {
   if (notification_bubble_) {
     notification_bubble_->bubble_view()->UpdateBubble();
     // Ensure that the notification buble is above the launcher/status area.
     notification_bubble_->bubble_view()->GetWidget()->StackAtTop();
     UpdateBubbleViewArrow(notification_bubble_->bubble_view());
   }
   if (system_bubble_) {
     system_bubble_->bubble_view()->UpdateBubble();
-    UpdateBubbleViewArrow(system_bubble_->bubble_view());
+    if (!ash::switches::UseAlternateShelfLayout())
+      UpdateBubbleViewArrow(system_bubble_->bubble_view());
   }
 }
 
 base::string16 SystemTray::GetAccessibleNameForTray() {
   return l10n_util::GetStringUTF16(IDS_ASH_STATUS_TRAY_ACCESSIBLE_NAME);
 }
 
 void SystemTray::HideBubbleWithView(const TrayBubbleView* bubble_view) {
   if (system_bubble_.get() && bubble_view == system_bubble_->bubble_view()) {
     DestroySystemBubble();
@@ skipping 60 matching lines @@
         ConvertPointToWidget(this, &point);
         arrow_offset = point.x();
       }
     }
     ShowDefaultViewWithOffset(BUBBLE_CREATE_NEW, arrow_offset);
   }
   return true;
 }
 
 }  // namespace ash