Plumb gesture source value through Blink.

components/test_runner/event_sender.cc

Index: components/test_runner/event_sender.cc
diff --git a/components/test_runner/event_sender.cc b/components/test_runner/event_sender.cc
index a2e55d58e54f67f67dc8ac9ea62e324be0a0b264..9c5fa8c9e344bf623afe21822f6f974d27d6a6e3 100644
--- a/components/test_runner/event_sender.cc
+++ b/components/test_runner/event_sender.cc
@@ -1657,6 +1657,7 @@ void EventSender::DumpFilenameBeingDragged() {
 void EventSender::GestureFlingCancel() {
   WebGestureEvent event;
   event.type = WebInputEvent::GestureFlingCancel;
+  event.sourceDevice = blink::WebGestureDeviceTouchpad;

[tdresser, 2015/10/14 17:18:56]

In an ideal world I think we'd have GestureFlingCancel take a parameter
indicating the source device in the same way as GestureFlingStart.

I suppose if it doesn't matter this is fine. Maybe add a note that it doesn't
matter?

[wjmaclean, 2015/10/14 18:03:28]

I'll add a not for now. It's a bunch of additional plumbing, and generally
GestureFlingCancel gets called all over the place, as a "just in case" sort of
thing, so I don't know if having to specify a source device mightn't get
cumbersom.

   event.timeStampSeconds = GetCurrentEventTimeSec();
 
   if (force_layout_on_events_)