Split out the extensions gin::Runner implementation into a separate class.

Split out the extensions gin::Runner implementation into a separate class.

The gin::Runner should be destroyed when the JS context is so that its
weak pointers are invalidated and any outstanding callbacks that
interact with the JS context can detect its destruction. Currently,
ScriptContext implements gin::Runner but is not immediately destroyed
when the JS context is. This CL moves this gin::Runner implementation
into a separate class which is destroyed when the ScriptContext is
invalidated.

Committed: https://crrev.com/de54a47ebf037458201dd5a36af885f078a8c861
Cr-Commit-Position: refs/heads/master@{#311358}

[Sam McNally, 2015-01-13 04:41:55]

Patchset #1 (id:1) has been deleted

[Sam McNally, 2015-01-13 04:42:07]

Patchset #1 (id:20001) has been deleted

[Sam McNally, 2015-01-13 05:00:04]

Patchset #1 (id:40001) has been deleted

[Sam McNally, 2015-01-13 05:01:29]

sammc@chromium.org changed reviewers:
+ kalman@chromium.org

[not at google - send to devlin, 2015-01-13 20:21:16]

lgtm

[Sam McNally, 2015-01-13 22:48:26]

The CQ bit was checked by sammc@chromium.org

[commit-bot: I haz the power, 2015-01-13 22:49:34]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/831423005/60001

[commit-bot: I haz the power, 2015-01-13 23:17:05]

Committed patchset #1 (id:60001)

[commit-bot: I haz the power, 2015-01-13 23:17:55]

Patchset 1 (id:??) landed as
https://crrev.com/de54a47ebf037458201dd5a36af885f078a8c861
Cr-Commit-Position: refs/heads/master@{#311358}