HTMLPlugInElement: Use custom focus logic only when there is a plugin.

HTMLPlugInElement: Use custom focus logic only when there is a plugin.

This allows focus to enter and leave plugin placeholders, so that constituent
elements (such as a close button) can be keyboard-focused.

TEST=fast/plugins/plugin/placeholder-focus.html
BUG=364716
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=185290

[jbroman, 2014-11-12 21:25:26]

jbroman@chromium.org changed reviewers:
+ esprehn@chromium.org, mkwst@chromium.org

[Mike West, 2014-11-13 10:13:36]

LGTM.

[jbroman, 2014-11-13 14:16:59]

The CQ bit was checked by jbroman@chromium.org

[commit-bot: I haz the power, 2014-11-13 14:18:03]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/717193003/1

[commit-bot: I haz the power, 2014-11-13 14:19:57]

Committed patchset #1 (id:1) as 185290

[jbroman, 2014-11-14 18:17:44]

A revert of this CL (patchset #1 id:1) has been created in
https://codereview.chromium.org/729573002/ by jbroman@chromium.org.

The reason for reverting is: probable cause of use-after-free:
https://code.google.com/p/chromium/issues/detail?id=433357.