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

ui/views/examples/label_example.cc

Index: ui/views/examples/label_example.cc
diff --git a/ui/views/examples/label_example.cc b/ui/views/examples/label_example.cc
index 2f82a402b9706312264fe423a6afa8257551cf6b..239b4db95f27ec9d4d0d6cd237a8d8ddf29bff86 100644
--- a/ui/views/examples/label_example.cc
+++ b/ui/views/examples/label_example.cc
@@ -25,7 +25,7 @@ class PreferredSizeLabel : public Label {
   virtual ~PreferredSizeLabel();
 
   // Label:
-  virtual gfx::Size GetPreferredSize() OVERRIDE;
+  virtual gfx::Size GetPreferredSize() const OVERRIDE;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(PreferredSizeLabel);
@@ -37,7 +37,9 @@ PreferredSizeLabel::PreferredSizeLabel() : Label() {
 
 PreferredSizeLabel::~PreferredSizeLabel() {}
 
-gfx::Size PreferredSizeLabel::GetPreferredSize() { return gfx::Size(100, 40); }
+gfx::Size PreferredSizeLabel::GetPreferredSize() const {
+  return gfx::Size(100, 40);
+}
 
 }  // namespace