Make interface destructor virtual

In summary, do this:

-  ~FrameCountObserver() {}
+  virtual ~FrameCountObserver() {}

BUG=
R=mflodman@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/4099005

git-svn-id: http://webrtc.googlecode.com/svn/trunk@5148 4adac7df-926f-26a2-2b94-8c16560cd09d
1 file changed