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

ash/system/tray/tray_popup_header_button.cc

 // 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.
 
 #include "ash/system/tray/tray_popup_header_button.h"
 
 #include "ash/ash_constants.h"
 #include "ash/system/tray/tray_constants.h"
 #include "ui/base/resource/resource_bundle.h"
 #include "ui/gfx/canvas.h"
@@ skipping 31 matching lines @@
                       kFocusBorderColor,
                       gfx::Insets(1, 2, 2, 3)));
 }
 
 TrayPopupHeaderButton::~TrayPopupHeaderButton() {}
 
 const char* TrayPopupHeaderButton::GetClassName() const {
   return kViewClassName;
 }
 
-gfx::Size TrayPopupHeaderButton::GetPreferredSize() {
+gfx::Size TrayPopupHeaderButton::GetPreferredSize() const {
   return gfx::Size(ash::kTrayPopupItemHeight, ash::kTrayPopupItemHeight);
 }
 
 void TrayPopupHeaderButton::OnPaintBorder(gfx::Canvas* canvas) {
   // Just the left border.
   const int kBorderHeight = 25;
   int padding = (height() - kBorderHeight) / 2;
   canvas->FillRect(gfx::Rect(0, padding, 1, height() - padding * 2),
       ash::kBorderDarkColor);
 }
 
 void TrayPopupHeaderButton::StateChanged() {
   SchedulePaint();
 }
 
 }  // namespace ash