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

ui/views/examples/double_split_view_example.cc

Index: ui/views/examples/double_split_view_example.cc
diff --git a/ui/views/examples/double_split_view_example.cc b/ui/views/examples/double_split_view_example.cc
index 90771d2b5de4fe4049d947ecb04dfabe5504c56f..8ff40df66a8541e644936d83612a6a184d10346a 100644
--- a/ui/views/examples/double_split_view_example.cc
+++ b/ui/views/examples/double_split_view_example.cc
@@ -22,7 +22,7 @@ class SplittedView : public View {
   void SetColor(SkColor from, SkColor to);
 
   // View:
-  virtual gfx::Size GetMinimumSize() OVERRIDE;
+  virtual gfx::Size GetMinimumSize() const OVERRIDE;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(SplittedView);
@@ -39,7 +39,7 @@ void SplittedView::SetColor(SkColor from, SkColor to) {
   set_background(Background::CreateVerticalGradientBackground(from, to));
 }
 
-gfx::Size SplittedView::GetMinimumSize() {
+gfx::Size SplittedView::GetMinimumSize() const {
   return gfx::Size(10, 10);
 }