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

ui/touch_selection/touch_selection_controller.cc

Index: ui/touch_selection/touch_selection_controller.cc
diff --git a/ui/touch_selection/touch_selection_controller.cc b/ui/touch_selection/touch_selection_controller.cc
index 90f7c6241580f66532ff678d360f070a8fa82bc3..9f463711bc6582f7294ee76210bea4a5ca5b61d3 100644
--- a/ui/touch_selection/touch_selection_controller.cc
+++ b/ui/touch_selection/touch_selection_controller.cc
@@ -231,6 +231,23 @@ bool TouchSelectionController::WillHandleLongPressEvent(
   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;