Change ScriptInjection to work with WebLocalFrames.

Change ScriptInjection to work with WebLocalFrames.

This is to help unblock some of the Blink work to move local frame only
APIs off WebFrame. Strictly speaking, all that was required to unblock
this bug was to manually coerce the WebFrame to a WebLocalFrame for the
call to setIsolatedWorldHumanReadableName.

However, it never makes sense to inject script on a remote frame, so
I've updated ScriptInjection to just work with local frames where
possible. Code that uses ScriptInjection now does the type coercion at
the class boundary. As extensions code is gradually updated to
understand out-of-process iframes, these manual type coercions should
disappear.

BUG=416659
Committed: https://crrev.com/2e44917894a92a0d6fb0e56e3220811f811d1c8e
Cr-Commit-Position: refs/heads/master@{#296345}

[dcheng, 2014-09-23 07:28:24]

dcheng@chromium.org changed reviewers:
+ yoz@chromium.org

[dcheng, 2014-09-23 17:14:58]

If anyone on the extensions team would like to sit down some time and figure out
how this code needs to be restructured for OOPI, I'd be more than happy to chat.

[dcheng, 2014-09-23 17:25:33]

(Also, this is blocking https://codereview.chromium.org/595713002 from landing.)

[Yoyo Zhou, 2014-09-23 23:20:25]

LGTM, seems reasonable, but I'm not really familiar with this side of things.

[dcheng, 2014-09-24 03:46:49]

Do you have any recommendations for who to talk to about these sort of issues
then?

[dcheng, 2014-09-24 03:46:53]

The CQ bit was checked by dcheng@chromium.org

[commit-bot: I haz the power, 2014-09-24 03:47:33]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/594043002/1

[commit-bot: I haz the power, 2014-09-24 04:31:06]

Committed patchset #1 (id:1) as 57de315ec54e7bb8ca7f76bb1313880b61e99e02

[commit-bot: I haz the power, 2014-09-24 04:31:48]

Patchset 1 (id:??) landed as
https://crrev.com/2e44917894a92a0d6fb0e56e3220811f811d1c8e
Cr-Commit-Position: refs/heads/master@{#296345}