Ensure Multi-finger tap generates both GestureScrollBegin and GestureScrollEnd.

Ensure Multi-finger tap generates both GestureScrollBegin and GestureScrollEnd.

There are two possible solutions to this bug:
1. Add a GestureScrollBegin.
2. Create a new state which allows scrolling but not tapping, and transition
   to that state on the release of a finger during multi-finger tap.

Option 1 is significantly simpler, and doesn't make the GR state machine any
more complicated. Option 2 prevents sending GestureScrollBegin and
GestureScrollEnd events which may not be accompanied by any GestureScrollUpdate
events.

I believe that option 1 is the correct choice here.

BUG=350121
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=256004

[sadrul, 2014-03-07 18:07:06]

https://codereview.chromium.org/189583007/diff/1/ui/events/gestures/gesture_s...
File ui/events/gestures/gesture_sequence.cc (right):

https://codereview.chromium.org/189583007/diff/1/ui/events/gestures/gesture_s...
ui/events/gestures/gesture_sequence.cc:655: set_state(GS_SCROLL);
Do you need the same change here, and in lines ~669, ~678, ~696, ~709?

[tdresser, 2014-03-07 19:23:26]

https://codereview.chromium.org/189583007/diff/1/ui/events/gestures/gesture_s...
File ui/events/gestures/gesture_sequence.cc (right):

https://codereview.chromium.org/189583007/diff/1/ui/events/gestures/gesture_s...
ui/events/gestures/gesture_sequence.cc:655: set_state(GS_SCROLL);
On 2014/03/07 18:07:07, sadrul wrote:
> Do you need the same change here, and in lines ~669, ~678, ~696, ~709?

Absolutely. Done.

[sadrul, 2014-03-10 03:54:52]

lgtm

https://codereview.chromium.org/189583007/diff/20001/ui/events/gestures/gestu...
File ui/events/gestures/gesture_sequence.cc (right):

https://codereview.chromium.org/189583007/diff/20001/ui/events/gestures/gestu...
ui/events/gestures/gesture_sequence.cc:639: set_state(GS_SCROLL);
It may make sense to have a 'TransitionToScrollState()' for these 4 lines.

[tdresser, 2014-03-10 12:36:38]

https://codereview.chromium.org/189583007/diff/20001/ui/events/gestures/gestu...
File ui/events/gestures/gesture_sequence.cc (right):

https://codereview.chromium.org/189583007/diff/20001/ui/events/gestures/gestu...
ui/events/gestures/gesture_sequence.cc:639: set_state(GS_SCROLL);
On 2014/03/10 03:54:52, sadrul wrote:
> It may make sense to have a 'TransitionToScrollState()' for these 4 lines.

Done. Named "StartRailFreeScroll," to indicate that it doesn't merely perform a
state change.

[tdresser, 2014-03-10 12:36:43]

The CQ bit was checked by tdresser@chromium.org

[commit-bot: I haz the power, 2014-03-10 12:37:28]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/tdresser@chromium.org/189583007/40001

[commit-bot: I haz the power, 2014-03-10 13:05:56]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/tdresser@chromium.org/189583007/40001

[commit-bot: I haz the power, 2014-03-10 14:20:41]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/tdresser@chromium.org/189583007/40001

[commit-bot: I haz the power, 2014-03-10 15:37:41]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/tdresser@chromium.org/189583007/40001

[commit-bot: I haz the power, 2014-03-10 17:35:41]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/tdresser@chromium.org/189583007/40001

[commit-bot: I haz the power, 2014-03-10 19:13:45]

Change committed as 256004