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

ui/message_center/views/message_center_button_bar.cc

Index: ui/message_center/views/message_center_button_bar.cc
diff --git a/ui/message_center/views/message_center_button_bar.cc b/ui/message_center/views/message_center_button_bar.cc
index a85fd183eb52260d4e8a0f582241ccd1eb4dd71a..c889490a4a0b515900045bee7b06d8c3a1407990 100644
--- a/ui/message_center/views/message_center_button_bar.cc
+++ b/ui/message_center/views/message_center_button_bar.cc
@@ -51,7 +51,7 @@ class NotificationCenterButton : public views::ToggleImageButton {
 
  protected:
   // Overridden from views::View:
-  virtual gfx::Size GetPreferredSize() OVERRIDE;
+  virtual gfx::Size GetPreferredSize() const OVERRIDE;
 
  private:
   gfx::Size size_;
@@ -83,7 +83,7 @@ NotificationCenterButton::NotificationCenterButton(
       gfx::Insets(1, 2, 2, 2)));
 }
 
-gfx::Size NotificationCenterButton::GetPreferredSize() { return size_; }
+gfx::Size NotificationCenterButton::GetPreferredSize() const { return size_; }
 
 // MessageCenterButtonBar /////////////////////////////////////////////////////
 ///////////////////////////////////////////////////////////////////////////////