Drag and drop cleans up touch sequences from the source window.

ui/events/gestures/motion_event_aura.cc

 // Copyright 2014 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/events/gestures/motion_event_aura.h"
 
 #include "base/logging.h"
 #include "ui/events/gesture_detection/gesture_configuration.h"
 
 namespace ui {
@@ skipping 46 matching lines @@
 
 MotionEventAura::MotionEventAura() {}
 
 MotionEventAura::~MotionEventAura() {}
 
 bool MotionEventAura::OnTouch(const TouchEvent& touch) {
   int index = FindPointerIndexOfId(touch.touch_id());
   bool pointer_id_is_active = index != -1;
 
   if (touch.type() == ET_TOUCH_PRESSED && pointer_id_is_active) {
-    // TODO(tdresser): This should return false (or NOTREACHED()), and
-    // ignore the touch; however, there is at least one case where we
-    // need to allow a touch press from a currently used touch id. See
-    // crbug.com/446852 for details.
-
-    // Cancel the existing touch, before handling the touch press.
-    TouchEvent cancel(ET_TOUCH_CANCELLED, gfx::Point(), touch.touch_id(),
-                      touch.time_stamp());
-    cancel.set_location_f(touch.location_f());
-    cancel.set_root_location_f(touch.location_f());
-    OnTouch(cancel);
-    CleanupRemovedTouchPoints(cancel);
-    DCHECK_EQ(-1, FindPointerIndexOfId(touch.touch_id()));
+    // TODO(tdresser): This should be NOTREACHED() - crbug.com/610423.
+    return false;
   } else if (touch.type() != ET_TOUCH_PRESSED && !pointer_id_is_active) {
-    // We could have an active touch stream transfered to us, resulting in touch
-    // move or touch up events without associated touch down events. Ignore
-    // them.
+    // When a window begins capturing touch events, we could have an active
+    // touch stream transfered to us, resulting in touch move or touch up events
+    // without associated touch down events. Ignore them.
     return false;
   }
 
   if (touch.type() == ET_TOUCH_MOVED && touch.x() == GetX(index) &&
       touch.y() == GetY(index)) {
     return false;
   }
 
   switch (touch.type()) {
     case ET_TOUCH_PRESSED:
@@ skipping 86 matching lines @@
 
 int MotionEventAura::GetIndexFromId(int id) const {
   int index = FindPointerIndexOfId(id);
   // TODO(tdresser): remove these checks once crbug.com/525189 is fixed.
   CHECK_GE(index, 0);
   CHECK_LT(index, static_cast<int>(GetPointerCount()));
   return index;
 }
 
 }  // namespace ui