Fix regression where mouse hover effect is absent on the browser action chevron

Fix regression where mouse hover effect is absent on the browser action chevron

It looks like a SetBorder(NULL) crept into
https://codereview.chromium.org/324393002, and the result is that the chevron
hover effect (i.e., draw a border) is overridden. Remove the call to
SetBorder().

BUG=407518
Committed: https://crrev.com/df431f0380f87e053a79f58dc72d0040153076ff
Cr-Commit-Position: refs/heads/master@{#292158}

[Devlin, 2014-08-26 18:03:37]

rdevlin.cronin@chromium.org changed reviewers:
+ finnur@chromium.org, pkasting@chromium.org

[Devlin, 2014-08-26 18:03:37]

Finnur and Peter, please take a look when you can.  It doesn't look like we need
this, but was there a reason it was added?  (Combing through the review, I can't
find one... but that was a *big* review, so I might have missed it.)

[Peter Kasting, 2014-08-26 18:06:20]

I have no objections, but Finnur is the one who would know better.  LGTM if he
approves.

[Finnur, 2014-08-27 10:46:39]

LGTM

I totally didn't remember adding this line so I dug up how it could happen.

What I found was that erg converted the code to use ChevronMenuButton and at the
same time removed the line in question:
https://codereview.chromium.org/298813002/diff/230001/chrome/browser/ui/views...
This happened shortly before I checked in my CL so I'm guessing it must be the
result of a bad merge.

Thanks for fixing!

[Devlin, 2014-08-27 13:34:03]

The CQ bit was checked by rdevlin.cronin@chromium.org

[commit-bot: I haz the power, 2014-08-27 13:35:34]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/rdevlin.cronin@chromium.org/492373004/1

[commit-bot: I haz the power, 2014-08-27 14:42:40]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  android_clang_dbg on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/android_clang_d...)
  android_dbg_tests_recipe on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/android_dbg_tes...)

[commit-bot: I haz the power, 2014-08-27 15:37:40]

Committed patchset #1 (id:1) as a56fbbaf0fa2be5b500573e0966346a9e0156727

[commit-bot: I haz the power, 2014-09-10 02:51:53]

Patchset 1 (id:??) landed as
https://crrev.com/df431f0380f87e053a79f58dc72d0040153076ff
Cr-Commit-Position: refs/heads/master@{#292158}