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

ui/base/gestures/gesture_sequence.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 "ui/base/gestures/gesture_sequence.h"
 
 #include <cmath>
 
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
@@ skipping 624 matching lines @@
                                              float x_velocity,
                                              float y_velocity) {
   float railed_x_velocity = x_velocity;
   float railed_y_velocity = y_velocity;
 
   if (scroll_type_ == ST_HORIZONTAL)
     railed_y_velocity = 0;
   else if (scroll_type_ == ST_VERTICAL)
     railed_x_velocity = 0;
 
-  // TODO(rjkroege): It is conceivable that we could suppress sending the
-  // GestureScrollEnd if it is immediately followed by a GestureFlingStart.
-  gestures->push_back(CreateGestureEvent(
-      GestureEventDetails(ui::ET_GESTURE_SCROLL_END, 0, 0),
-      location,
-      flags_,
-      base::Time::FromDoubleT(point.last_touch_time()),
-      1 << point.touch_id()));
-
   if (railed_x_velocity != 0 || railed_y_velocity != 0) {
     // TODO(sad|rjkroege): fling-curve is currently configured to work well with
     // touchpad scroll-events. This curve needs to be adjusted to work correctly
     // with both touchpad and touchscreen. Until then, scale quadratically.
     // http://crbug.com/120154
     const float velocity_scaling  = 1.f / 900.f;
 
     gestures->push_back(CreateGestureEvent(
         GestureEventDetails(ui::ET_SCROLL_FLING_START,
             velocity_scaling * railed_x_velocity * fabsf(railed_x_velocity),
             velocity_scaling * railed_y_velocity * fabsf(railed_y_velocity)),
         location,
         flags_,
         base::Time::FromDoubleT(point.last_touch_time()),
         1 << point.touch_id()));
+  } else {
+    gestures->push_back(CreateGestureEvent(
+        GestureEventDetails(ui::ET_GESTURE_SCROLL_END, 0, 0),
+        location,
+        flags_,
+        base::Time::FromDoubleT(point.last_touch_time()),
+        1 << point.touch_id()));
   }
 }
 
 void GestureSequence::AppendScrollGestureUpdate(const GesturePoint& point,
                                                 const gfx::Point& location,
                                                 Gestures* gestures) {
   gfx::Point current_center = bounding_box_.CenterPoint();
   int dx = current_center.x() - bounding_box_last_center_.x();
   int dy = current_center.y() - bounding_box_last_center_.y();
   if (scroll_type_ == ST_HORIZONTAL)
@@ skipping 349 matching lines @@
     return;
 
   // Since long press timer has been started, there should be a non-NULL point.
   const GesturePoint* point = GetPointByPointId(0);
   if (!ui::gestures::IsInsideManhattanSquare(point->first_touch_position(),
       event.GetLocation()))
     long_press_timer_->Stop();
 }
 
 }  // namespace ui