Fix a bug that snackbar is drawn under navigagion bar

Fix a bug that snackbar is drawn under navigagion bar

In L apps are able to extend itself under the navigation bar. Yet this
feature is not needed in enhanced bookmarks, and it caused a UI bug with
snackbar.

BUG=508873
Committed: https://crrev.com/5476228290d10bb5d02ffdee8e096c3a3a77637a
Cr-Commit-Position: refs/heads/master@{#339800}

[Ian Wen, 2015-07-21 22:46:55]

ianwen@chromium.org changed reviewers:
+ newt@chromium.org

[newt (away), 2015-07-21 22:52:47]

lgtm

[Ian Wen, 2015-07-21 22:53:07]

The CQ bit was checked by ianwen@chromium.org

[commit-bot: I haz the power, 2015-07-21 22:54:49]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1250853005/1

[commit-bot: I haz the power, 2015-07-22 00:49:20]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-07-22 00:50:14]

Patchset 1 (id:??) landed as
https://crrev.com/5476228290d10bb5d02ffdee8e096c3a3a77637a
Cr-Commit-Position: refs/heads/master@{#339800}