Bug 2372180: pass multi-touch events from browser to webkit.

Since the UI uses multi-touch for zooming, the event is passed to webkit
only when the webpage doesn't allow zooming.
1. Updated the data structure TouchEventData in WebViewCore.java
   to take multiple points and used it everywhere.
2. Added a passMultiTouchToWebkit() function to do what its name means.
3. Added the multi-point touch support to dumprendertree.

Change-Id: Iafc1aa7b21a587ad26efd2f124b9a66316297ab8