Revert of [OSX] Allow one zoom bubble to override another.

Revert of [OSX] Allow one zoom bubble to override another. (patchset #1 id:1 of https://codereview.chromium.org/886883002/)

Reason for revert:
Causes window flickering:
https://code.google.com/p/chromium/issues/detail?id=455184

Original issue's description:
> [OSX] Allow one zoom bubble to override another.
>
> At present, if a user changes zoom on OSX while the zoom bubble is
> already being shown, the new zoom bubble (with the most up to date
> information) is not shown. This CL changes this behaviour by allowing
> a new zoom bubble to be created, and replace the existing one.
>
> Example: load a PDF and repeatedly click the zoom +/- controls in the
> lower-right corner of the viewer.
>
> BUG=444995
>
> Committed: https://crrev.com/84567ceada9f89c8e962d18ab494b1d1bb5a3830
> Cr-Commit-Position: refs/heads/master@{#314147}

TBR=rohitrao@chromium.org,wjmaclean@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=444995
Committed: https://crrev.com/7f84e128cc1e81d046423e8329c3f1767946f05e
Cr-Commit-Position: refs/heads/master@{#314608}

[erikchen, 2015-02-04 19:32:21]

Created Revert of [OSX] Allow one zoom bubble to override another.

[commit-bot: I haz the power, 2015-02-04 19:33:24]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/897923002/1

[commit-bot: I haz the power, 2015-02-04 19:34:40]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-02-04 19:35:31]

Patchset 1 (id:??) landed as
https://crrev.com/7f84e128cc1e81d046423e8329c3f1767946f05e
Cr-Commit-Position: refs/heads/master@{#314608}