Fixing TouchEvent.supported

It was reporting as not being supported because there's no Window.ontouch, but the constructor is now working.

TBR
BUG=

Review URL: https://codereview.chromium.org//141113006

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@31907 260f80e4-7a28-3924-810f-c04153c831b5
4 files changed