Fix Custom Action Bar for custom tabs on tablet

Fix Custom Action Bar for custom tabs on tablet

Custom tabs on tablet is special in that it does not have a tab strip.
Therefore ContextualMenuBar will calculate the wrong offset when
animating the bar.

BUG=510284
Committed: https://crrev.com/402517c6677e81adf93d11462aeb1b86bfbf9f8a
Cr-Commit-Position: refs/heads/master@{#343437}

[Ian Wen, 2015-08-14 00:38:12]

ianwen@chromium.org changed reviewers:
+ dtrainor@chromium.org, yusufo@chromium.org

[Ian Wen, 2015-08-14 00:38:13]

dtrainor@chromium.org: Please review changes in 

yusufo@chromium.org: Please review changes in

[David Trainor- moved to gerrit, 2015-08-14 00:39:46]

lgtm

[Ian Wen, 2015-08-14 17:35:20]

The CQ bit was checked by ianwen@chromium.org

[commit-bot: I haz the power, 2015-08-14 17:35:28]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1292693002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1292693002/1

[commit-bot: I haz the power, 2015-08-14 18:21:49]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-08-14 18:22:24]

Patchset 1 (id:??) landed as
https://crrev.com/402517c6677e81adf93d11462aeb1b86bfbf9f8a
Cr-Commit-Position: refs/heads/master@{#343437}