[WIP] Allow scroll events to permanently change the default gesture handler in RootView

ash/frame/caption_buttons/frame_size_button.cc

Index: ash/frame/caption_buttons/frame_size_button.cc
diff --git a/ash/frame/caption_buttons/frame_size_button.cc b/ash/frame/caption_buttons/frame_size_button.cc
index 1399453ffdcfff07c8b357fc88001905a58fac16..56f70f65300de3b5cd23f7534da23262f77cfbbc 100644
--- a/ash/frame/caption_buttons/frame_size_button.cc
+++ b/ash/frame/caption_buttons/frame_size_button.cc
@@ -120,8 +120,7 @@ void FrameSizeButton::OnGestureEvent(ui::GestureEvent* event) {
 
   if (event->type() == ui::ET_GESTURE_TAP ||
       event->type() == ui::ET_GESTURE_SCROLL_END ||
-      event->type() == ui::ET_SCROLL_FLING_START ||
-      event->type() == ui::ET_GESTURE_END) {

[tdresser, 2014/07/24 18:17:22]

This changes behavior, doesn't it?
Are we ok with the behavior change?

[sadrul, 2014/07/24 19:12:13]

Looks like the code starts doing things in response to TAP_DOWN and/or
SCROLL_BEGIN/UPDATE. So TAP_CANCEL and SCROLL_END should be sufficient for this.
It doesn't look like this View processes GESTURE_BEGIN event, so it shouldn't
need to do anything in response to GESTURE_END.

[tdresser, 2014/07/24 19:16:44]

Shouldn't it also listen to LONG_TAP?

[sadrul, 2014/07/24 19:21:34]

Good point. That will probably be necessary here, yes.

[tdanderson, 2014/07/25 17:16:10]

Thanks for pointing this out.

+      event->type() == ui::ET_SCROLL_FLING_START) {
     if (CommitSnap(*event)) {
       if (event->type() == ui::ET_GESTURE_TAP) {
         TouchUMA::GetInstance()->RecordGestureAction(