Don't create zero-velocity GestureFlingStarts.

content/browser/renderer_host/render_widget_host_input_event_router.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/renderer_host/render_widget_host_input_event_router.h"
 
 #include "base/debug/dump_without_crashing.h"
 #include "cc/quads/surface_draw_quad.h"
 #include "cc/surfaces/surface_id_allocator.h"
 #include "cc/surfaces/surface_manager.h"
@@ skipping 149 matching lines @@
   // TODO(wjmaclean): Initialize latency info correctly for OOPIFs.
   // https://crbug.com/613628
   ui::LatencyInfo latency_info;
   target->ProcessMouseWheelEvent(*event, latency_info);
 }
 
 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";
       break;
     case blink::WebGestureDeviceTouchpad:
       RouteTouchpadGestureEvent(root_view, event, latency);
       break;
     case blink::WebGestureDeviceTouchscreen:
       RouteTouchscreenGestureEvent(root_view, event, latency);
       break;
@@ skipping 151 matching lines @@
   if (!touchpad_gesture_target_.target)
     return;
 
   // TODO(mohsen): Add tests to check event location.
   event->x += touchpad_gesture_target_.delta.x();
   event->y += touchpad_gesture_target_.delta.y();
   touchpad_gesture_target_.target->ProcessGestureEvent(*event, latency);
 }
 
 }  // namespace content