Implement cancel() API on a Notification object so that script can cancel or ...

chrome/browser/notifications/balloon.h

Index: chrome/browser/notifications/balloon.h
===================================================================
--- chrome/browser/notifications/balloon.h	(revision 30967)
+++ chrome/browser/notifications/balloon.h	(working copy)
@@ -32,7 +32,7 @@
   virtual void RepositionToBalloon() = 0;
 
   // Close the view.
-  virtual void Close() = 0;
+  virtual void Close(bool by_user) = 0;
 };
 
 // Represents a Notification on the screen.
@@ -65,9 +65,16 @@
   // to this object.
   void set_view(BalloonView* balloon_view);
 
+  // Shows the balloon.
   virtual void Show();
-  virtual void Close(bool by_user);
 
+  // Called when the balloon is closed, either by user (through the UI)
+  // or by a script.
+  virtual void OnClose(bool by_user);
+
+  // Called by script to cause the balloon to close.
+  virtual void CloseByScript();
+
  private:
   // Non-owned pointer to the profile.
   Profile* profile_;