Allow scrolling a page with selection after long-press on whitespace

ui/touch_selection/touch_selection_controller.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/touch_selection/touch_selection_controller.h"
 
 #include "base/auto_reset.h"
 #include "base/logging.h"
 #include "base/metrics/histogram_macros.h"
 
@@ skipping 213 matching lines @@
     return true;
 
   longpress_drag_selector_.OnLongPressEvent(event_time, location);
   response_pending_input_event_ = LONG_PRESS;
   ShowSelectionHandlesAutomatically();
   ShowInsertionHandleAutomatically();
   ForceNextUpdateIfInactive();
   return false;
 }
 
+void TouchSelectionController::OnScrollBeginEvent() {
+  // If a scroll happens after a long-press on an empty area, the long-press

[mfomitchev, 2016/01/04 18:58:44]

Can we rephrase to be a bit more explicit, e.g.:
If there is an active selection, and the user performs a long press that does
not trigger a new selection (e.g. a long press on an empty area)...

[mohsen, 2016/01/04 19:23:05]

Done.

+  // will not change the selection, however the scroll will move the selection.
+  // In this case we might think incorrectly that the selection change was due

[mfomitchev, 2016/01/04 18:58:44]

Can we replace "might" with "will" here?
Also, perhaps add "(see ActivateSelectionIfNecessary())" in the end of the
sentence?

[mohsen, 2016/01/04 19:23:05]

Done.

+  // to long-press and will activate touch selection and start long-press drag
+  // gesture. To prevent this, we need to reset the state of touch selection
+  // controller and long-press drag selector.
+  // TODO(mohsen): Remove this workaround when we have enough information about
+  // the cause of a selection change (see https://crbug.com/571897).
+  longpress_drag_selector_.OnScrollBeginEvent();
+  response_pending_input_event_ = INPUT_EVENT_TYPE_NONE;
+  if (active_status_ == INACTIVE) {
+    activate_insertion_automatically_ = false;
+    activate_selection_automatically_ = false;
+  }
+}
+
 void TouchSelectionController::AllowShowingFromCurrentSelection() {
   if (active_status_ != INACTIVE)
     return;
 
   activate_selection_automatically_ = true;
   activate_insertion_automatically_ = true;
   if (GetStartPosition() != GetEndPosition()) {
     OnSelectionChanged();
   } else if (start_orientation_ == TouchHandleOrientation::CENTER &&
              selection_editable_) {
@@ skipping 417 matching lines @@
     base::TimeDelta duration = base::TimeTicks::Now() - selection_start_time_;
     UMA_HISTOGRAM_CUSTOM_TIMES("Event.TouchSelection.WasDraggedDuration",
                                duration,
                                base::TimeDelta::FromMilliseconds(500),
                                base::TimeDelta::FromSeconds(60),
                                60);
   }
 }
 
 }  // namespace ui