Introduces a new scrollbar for message_center.

ui/views/controls/scrollbar/scroll_bar.h

Index: ui/views/controls/scrollbar/scroll_bar.h
diff --git a/ui/views/controls/scrollbar/scroll_bar.h b/ui/views/controls/scrollbar/scroll_bar.h
index 5b534d6c68cec9a0dcba5b74954fd3cbef434fd3..738a609167322efca494f330cb22e82c962f2e00 100644
--- a/ui/views/controls/scrollbar/scroll_bar.h
+++ b/ui/views/controls/scrollbar/scroll_bar.h
@@ -86,6 +86,14 @@ class VIEWS_EXPORT ScrollBar : public View {
   // is the height for a horizontal scrollbar.
   virtual int GetLayoutSize() const = 0;
 
+  // Get the actually visible width or height for this scrollbar. Default is
+  // same as GetLayoutSize(). This value can be different from GetLayoutSize()
+  // if the scrollbar overlaps its contents.
+  virtual int GetVisibleSize() const;

[sadrul, 2013/06/04 19:03:24]

Call this GetContentOverlapSize() instead. That would make it much easier to
follow what's happening.

[Jun Mukai, 2013/06/04 20:52:38]

Done.

+
+  virtual void OnMouseEnteredScrollView(const ui::MouseEvent& event);
+  virtual void OnMouseExitedScrollView(const ui::MouseEvent& event);
+
  protected:
   // Create new scrollbar, either horizontal or vertical. These are protected
   // since you need to be creating either a NativeScrollBar or a