Do not activate system tray bubble by default

ash/common/system/tray/tray_background_view.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/common/system/tray/tray_background_view.h"
 
 #include "ash/common/material_design/material_design_controller.h"
 #include "ash/common/shelf/shelf_constants.h"
 #include "ash/common/shelf/wm_shelf.h"
 #include "ash/common/shelf/wm_shelf_util.h"
@@ skipping 230 matching lines @@
   views::BoxLayout* layout = new views::BoxLayout(orientation, 0, 0, 0);
   layout->SetDefaultFlex(1);
   views::View::SetLayoutManager(layout);
   PreferredSizeChanged();
 }
 
 ////////////////////////////////////////////////////////////////////////////////
 // TrayBackgroundView
 
 TrayBackgroundView::TrayBackgroundView(WmShelf* wm_shelf)
-    : wm_shelf_(wm_shelf),
+    : ActionableView(nullptr),
+      wm_shelf_(wm_shelf),
       tray_container_(NULL),
       shelf_alignment_(SHELF_ALIGNMENT_BOTTOM),
       background_(NULL),
       draw_background_as_active_(false),
       is_separator_visible_(false),
       widget_observer_(new TrayWidgetObserver(this)) {
   DCHECK(wm_shelf_);
   set_notify_enter_exit_on_child(true);
 
   tray_container_ = new TrayContainer(shelf_alignment_);
@@ skipping 300 matching lines @@
   paint.setAntiAlias(true);
 
   const gfx::Rect bounds = horizontal_shelf ? gfx::Rect(x, y, width, height)
                                             : gfx::Rect(y, x, height, width);
   gfx::RectF rect(gfx::ScaleRect(gfx::RectF(bounds), scale));
   canvas->DrawLine(horizontal_shelf ? rect.top_right() : rect.bottom_left(),
                    rect.bottom_right(), paint);
 }
 
 }  // namespace ash