Remove support for the obsolete <isindex> tag.

Remove support for the obsolete <isindex> tag.

This patch removes all special-casing for the <isindex> tag; it
now behaves exactly like <foo> in all respects. This additionally
means that we can remove the special-casing for forms containing
<input name="isindex"> as their first element.

The various tests for <isindex> have been deleted, with the
exception of the imported HTML5Lib tests. It's not clear that
we should send them patches to remove the <isindex> tests, at
least not while the element is (an obsolete) part of HTML5, and
supported by other vendors.

I've just landed failing test results here. That seems like
the right thing to do.

"Intent to Remove" discussion: https://groups.google.com/a/chromium.org/d/msg/blink-dev/14q_I06gwg8/0a3JI0kjbC0J

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=168010

[Mike West, 2014-02-26 10:55:40]

Hi Eric, Dimitri, and Jochen! WDYT (particularly about the failing HTML5Lib
tests)? 

-mike

[eseidel, 2014-02-26 18:58:29]

lgtm

[commit-bot: I haz the power, 2014-02-26 18:58:43]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/mkwst@chromium.org/96653004/70001

[commit-bot: I haz the power, 2014-02-26 21:45:51]

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

[commit-bot: I haz the power, 2014-02-26 21:45:51]

Retried try job too often on mac_blink_rel for step(s) webkit_tests
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=mac_blink_...

[Mike West, 2014-02-27 08:17:09]

The CQ bit was checked by mkwst@chromium.org

[commit-bot: I haz the power, 2014-02-27 08:17:26]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/mkwst@chromium.org/96653004/90001

[commit-bot: I haz the power, 2014-02-27 10:32:55]

Change committed as 168010