Fix a bug in pinch handling of the tab switcher.

The whole tab stack disappears when the user pinch all tabs together
and scroll to the top of the screen when we have multiple tabs.

This is caused by Y position of the stack sets to NaN, where there is
a division to 0 in the code.

BUG=670897
Committed: https://crrev.com/531c3255a45abfa9b6a8a621c76b88c1f5b21a73
Cr-Commit-Position: refs/heads/master@{#436457}

[xingliu, 2016-12-02 23:59:23]

The CQ bit was checked by xingliu@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2016-12-03 00:00:40]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[xingliu, 2016-12-03 00:01:27]

Description was changed from

==========
Fix a bug in pinch of the tab switcher.

The whole tab stack disappears when the user pinch and scroll to the
top.

This is caused by Y position of the stack sets to NaN, where there is
a division to 0 in the code.


BUG=670897
==========

to

==========
The whole tab stack disappears when the user pinch and scroll to the
top when we have multiple tabs.

This is caused by Y position of the stack sets to NaN, where there is
a division to 0 in the code.


BUG=670897
==========

[xingliu, 2016-12-03 00:02:58]

Description was changed from

==========
The whole tab stack disappears when the user pinch and scroll to the
top when we have multiple tabs.

This is caused by Y position of the stack sets to NaN, where there is
a division to 0 in the code.


BUG=670897
==========

to

==========
The whole tab stack disappears when the user pinch all tabs together
and scroll to the top of the screen when we have multiple tabs.

This is caused by Y position of the stack sets to NaN, where there is
a division to 0 in the code.


BUG=670897
==========

[xingliu, 2016-12-03 00:20:46]

xingliu@chromium.org changed reviewers:
+ dtrainor@chromium.org

[xingliu, 2016-12-03 00:20:47]

Fixed the stack disappearing bug when pinch.

[commit-bot: I haz the power, 2016-12-03 01:06:15]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2016-12-03 01:06:16]

Dry run: This issue passed the CQ dry run.

[David Trainor- moved to gerrit, 2016-12-05 21:38:09]

lgtm great catch!

[xingliu, 2016-12-05 22:52:07]

The CQ bit was checked by xingliu@chromium.org

[commit-bot: I haz the power, 2016-12-05 22:53:05]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-12-05 23:44:51]

CQ is committing da patch.

Bot data: {"patchset_id": 1, "attempt_start_ts": 1480978327082980, "parent_rev":
"1cf843c2c3e07421c73e2dcfc730d7281953453b", "commit_rev":
"98ad0de5105ceade35a7735e2f79e83c934bb5b5"}

[commit-bot: I haz the power, 2016-12-05 23:45:19]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-12-05 23:47:03]

Description was changed from

==========
The whole tab stack disappears when the user pinch all tabs together
and scroll to the top of the screen when we have multiple tabs.

This is caused by Y position of the stack sets to NaN, where there is
a division to 0 in the code.


BUG=670897
==========

to

==========
The whole tab stack disappears when the user pinch all tabs together
and scroll to the top of the screen when we have multiple tabs.

This is caused by Y position of the stack sets to NaN, where there is
a division to 0 in the code.

BUG=670897

Committed: https://crrev.com/531c3255a45abfa9b6a8a621c76b88c1f5b21a73
Cr-Commit-Position: refs/heads/master@{#436457}
==========

[commit-bot: I haz the power, 2016-12-05 23:47:04]

Patchset 1 (id:??) landed as
https://crrev.com/531c3255a45abfa9b6a8a621c76b88c1f5b21a73
Cr-Commit-Position: refs/heads/master@{#436457}