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 d6f8de72a29d6d06738e85070b22beba38f57406..5585db5237e6d3532f02c39ba69a699ca43ca254 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
@@ -167,6 +167,10 @@ 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";