gestures: Generate only either scroll-end or fling-start events at the end of a scroll gesture.

content/browser/renderer_host/render_widget_host_view_aura.cc

 // Copyright (c) 2012 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_view_aura.h"
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/command_line.h"
 #include "base/debug/trace_event.h"
@@ skipping 1300 matching lines @@
     delegate->HandleGestureBegin();
   }
 
   WebKit::WebGestureEvent gesture = MakeWebGestureEvent(event);
   if (event->type() == ui::ET_GESTURE_TAP_DOWN) {
     // Webkit does not stop a fling-scroll on tap-down. So explicitly send an
     // event to stop any in-progress flings.
     WebKit::WebGestureEvent fling_cancel = gesture;
     fling_cancel.type = WebKit::WebInputEvent::GestureFlingCancel;
     host_->ForwardGestureEvent(fling_cancel);
+  } else if (event->type() == ui::ET_SCROLL_FLING_START) {
+    // WebKit requires that a scroll ends first before a fling starts.

[rjkroege, 2012/08/09 16:51:06]

It is planned to remove this requirement on WebKit. Did you test without the
presence of this code? It is my intent that this ought to be removed from here
if it is currently necessary.

[sadrul, 2012/08/09 17:44:02]

Nice! My impression was that it was still necessary. But I tried without this
block of code, in debug and release builds on desktop, and on device, and scroll
with/without fling seems to work fine. So I have removed this change. Thanks!

+    WebKit::WebGestureEvent scroll_end = gesture;
+    gesture.type = WebKit::WebInputEvent::GestureScrollEnd;
+    host_->ForwardGestureEvent(scroll_end);
   }
 
   if (gesture.type != WebKit::WebInputEvent::Undefined) {
     host_->ForwardGestureEvent(gesture);
 
     if (event->type() == ui::ET_GESTURE_SCROLL_BEGIN ||
         event->type() == ui::ET_GESTURE_SCROLL_UPDATE ||
         event->type() == ui::ET_GESTURE_SCROLL_END) {
       RecordAction(UserMetricsAction("TouchscreenScroll"));
     } else if (event->type() == ui::ET_SCROLL_FLING_START) {
@@ skipping 324 matching lines @@
     RenderWidgetHost* widget) {
   return new RenderWidgetHostViewAura(widget);
 }
 
 // static
 void RenderWidgetHostViewPort::GetDefaultScreenInfo(WebScreenInfo* results) {
   GetScreenInfoForWindow(results, NULL);
 }
 
 }  // namespace content