Don't create zero-velocity GestureFlingStarts.

content/browser/renderer_host/render_widget_host_input_event_router.cc

Index: content/browser/renderer_host/render_widget_host_input_event_router.cc
diff --git a/content/browser/renderer_host/render_widget_host_input_event_router.cc b/content/browser/renderer_host/render_widget_host_input_event_router.cc
index 9786dad6d20708b7de81d7cef93b633ac84dfe5b..ca50c6184842f1888d45c5c0632583b4295c2f9b 100644
--- a/content/browser/renderer_host/render_widget_host_input_event_router.cc
+++ b/content/browser/renderer_host/render_widget_host_input_event_router.cc
@@ -173,6 +173,10 @@ void RenderWidgetHostInputEventRouter::RouteGestureEvent(
     RenderWidgetHostViewBase* root_view,
     blink::WebGestureEvent* event,
     const ui::LatencyInfo& latency) {
+  DCHECK(event->type != blink::WebInputEvent::GestureFlingStart ||
+         event->data.flingStart.velocityX != 0.0 ||
+         event->data.flingStart.velocityY != 0.0);
+
   switch (event->sourceDevice) {
     case blink::WebGestureDeviceUninitialized:
       NOTREACHED() << "Uninitialized device type is not allowed";