Fix <extensionoptions> setAutoSize call

Fix <extensionoptions> setAutoSize call

The browser plugin -internal-attach CL
(https://codereview.chromium.org/444813002/) was committed just
before the extension options autosizing animation CL
(https://codereview.chromium.org/480243003/), so a call to
guestViewInternal.setAutoSize() added in the second CL used a property
that no longer existed (this.instanceId). Rename the variable so that
the autosize call works again.

BUG=386842

[ericzeng, 2014-08-22 01:48:21]

PTAL, quick fix for a merge conflict

[Fady Samuel, 2014-08-22 01:51:24]

lgtm

[not at google - send to devlin, 2014-08-22 02:00:07]

lgtm

[ericzeng, 2014-08-22 02:00:32]

The CQ bit was checked by ericzeng@chromium.org

[commit-bot: I haz the power, 2014-08-22 02:02:32]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/ericzeng@chromium.org/496863004/1

[commit-bot: I haz the power, 2014-08-22 03:05:17]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  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, 2014-08-22 03:58:51]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-08-22 03:58:52]

Try jobs failed on following builders:
  android_dbg_tests_recipe on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/android_dbg_tes...)

[ericzeng, 2014-08-22 04:03:50]

The CQ bit was checked by ericzeng@chromium.org

[commit-bot: I haz the power, 2014-08-22 04:04:51]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/ericzeng@chromium.org/496863004/1

[jam, 2014-08-22 04:11:14]

On 2014/08/22 01:48:21, ericzeng wrote:
> PTAL, quick fix for a merge conflict

in the future, never CQ a quick fix. either you try it locally to confirm and
land manually, or revert immediately. the tree has been broken for 3 hours.

[commit-bot: I haz the power, 2014-08-22 05:00:28]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  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, 2014-08-22 05:03:48]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-08-22 05:03:49]

Try jobs failed on following builders:
  android_dbg_tests_recipe on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/android_dbg_tes...)