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

ui/views/controls/button/label_button.h

Index: ui/views/controls/button/label_button.h
diff --git a/ui/views/controls/button/label_button.h b/ui/views/controls/button/label_button.h
index dc34b7a4d91d4867b33b467d933b960f3bb71e32..b9a73f23b61490768025527a6eabe467ad9e7d0e 100644
--- a/ui/views/controls/button/label_button.h
+++ b/ui/views/controls/button/label_button.h
@@ -75,7 +75,7 @@ class VIEWS_EXPORT LabelButton : public CustomButton,
 
   // View:
   virtual void SetBorder(scoped_ptr<Border> border) OVERRIDE;
-  virtual gfx::Size GetPreferredSize() OVERRIDE;
+  virtual gfx::Size GetPreferredSize() const OVERRIDE;
   virtual void Layout() OVERRIDE;
   virtual const char* GetClassName() const OVERRIDE;
 
@@ -148,7 +148,7 @@ class VIEWS_EXPORT LabelButton : public CustomButton,
   bool explicitly_set_colors_[STATE_COUNT];
 
   // |min_size_| increases monotonically with the preferred size.
-  gfx::Size min_size_;
+  mutable gfx::Size min_size_;
   // |max_size_| may be set to clamp the preferred size.
   gfx::Size max_size_;