Remove UserScript support, which is not used by Chromium

Remove UserScript support, which is not used by Chromium

Though the Chromium/WebKit API exposes the addUserScript method, it's
only ever called by the TestRunner. Nearly all the tests under userscripts/
were simply testing the behavior of PageGroup::addUserScript, but since
Chromium doesn't use this in non-test code, these tests can safely be deleted.
Also deleted related code in Frame, FrameLoader, and various other addUser*
methods not used by Chromium or WebCore.

For those tests that were exercising addUserStylesheet, I've moved them to
LayoutTests/userstyles. For the few tests that were actually just testing
isolated world behavior, I've moved them to fast/events.

Besides deleting dead code, this patch gets rid of one usage of
temporary isolated worlds (see attached bug).

R=abarth
BUG=230460
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=148237

[abarth-chromium, 2013-04-11 20:49:42]

Great!  LGTM.

[commit-bot: I haz the power, 2013-04-11 20:57:59]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/adamk@chromium.org/14188004/3002

[commit-bot: I haz the power, 2013-04-11 21:04:31]

Presubmit check for 14188004-3002 failed and returned exit status -2001.
The presubmit check was hung. It took 360.0 seconds to execute and the time
limit is 360.0 seconds.

INFO:root:Found 29 file(s).

[adamk, 2013-04-11 23:02:37]

Committed patchset #2 manually as r148237 (presubmit successful).