Add support for sending touch events in DRT.

As part of this, make it possible for DRT to configure the timeout threshold between sending touch events to WebCore as the Layout Tests only synthesize single events, not a stream. Because of this, they often get dropped by the WebView for coming too quickly.

Skip the multi touch test as we don't support multi touch in the Browser.

Change-Id: I7b9830f43181fea33206825b49ef2e294269b4dd