views: Make view::Views::GetPreferredSize() const.

ash/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/system/tray/tray_background_view.h"
 
 #include "ash/ash_switches.h"
 #include "ash/root_window_controller.h"
 #include "ash/screen_util.h"
 #include "ash/shelf/shelf_layout_manager.h"
@@ skipping 211 matching lines @@
   UpdateLayout();
 }
 
 void TrayBackgroundView::TrayContainer::SetAlignment(ShelfAlignment alignment) {
   if (alignment_ == alignment)
     return;
   alignment_ = alignment;
   UpdateLayout();
 }
 
-gfx::Size TrayBackgroundView::TrayContainer::GetPreferredSize() {
+gfx::Size TrayBackgroundView::TrayContainer::GetPreferredSize() const {
   if (size_.IsEmpty())
     return views::View::GetPreferredSize();
   return size_;
 }
 
 void TrayBackgroundView::TrayContainer::ChildPreferredSizeChanged(
     views::View* child) {
   PreferredSizeChanged();
 }
 
@@ skipping 276 matching lines @@
     background_->set_alpha(kTrayBackgroundAlpha);
   SchedulePaint();
 }
 
 void TrayBackgroundView::UpdateBubbleViewArrow(
     views::TrayBubbleView* bubble_view) {
   // Nothing to do here.
 }
 
 }  // namespace ash