Fix a regression where the tab-modal signin flow wasn't shown.

Fix a regression where the tab-modal signin flow wasn't shown.

https://codereview.chromium.org/1781433002 changed some of the
constrained_window code and updated some callers, but not the tab-modal
signin flow. The modal was being created but not shown.

BUG=593091, 217034
Review URL: https://codereview.chromium.org/1815433002

Cr-Commit-Position: refs/heads/master@{#381778}
(cherry picked from commit 4588b6b41a9356338c1c2a2eea3bf11fb8647a35)

Committed: https://chromium.googlesource.com/chromium/src/+/8ef11436d4619a1292803a29f2623df4f2f44bf6

[apacible, 2016-03-23 23:16:25]

Description was changed from

==========
Fix a regression where the tab-modal signin flow wasn't shown.

https://codereview.chromium.org/1781433002 changed some of the
constrained_window code and updated some callers, but not the tab-modal
signin flow. The modal was being created but not shown.

BUG=593091,217034

Review URL: https://codereview.chromium.org/1815433002

Cr-Commit-Position: refs/heads/master@{#381778}
(cherry picked from commit 4588b6b41a9356338c1c2a2eea3bf11fb8647a35)
==========

to

==========
Fix a regression where the tab-modal signin flow wasn't shown.

https://codereview.chromium.org/1781433002 changed some of the
constrained_window code and updated some callers, but not the tab-modal
signin flow. The modal was being created but not shown.

BUG=593091,217034

Review URL: https://codereview.chromium.org/1815433002

Cr-Commit-Position: refs/heads/master@{#381778}
(cherry picked from commit 4588b6b41a9356338c1c2a2eea3bf11fb8647a35)

Committed:
https://chromium.googlesource.com/chromium/src/+/8ef11436d4619a1292803a29f262...
==========

[apacible, 2016-03-23 23:16:26]

Committed patchset #1 (id:1) manually as
8ef11436d4619a1292803a29f2623df4f2f44bf6.