Use the blink main thread isolate for v8 unit tests.

Use the blink main thread isolate for v8 unit tests.

The TestWebKitPlatformSupport will initialize it for us anyway, so use
it.

BUG=none
R=andrewhayden@chromium.org,haraken@chromium.org

Committed: https://crrev.com/1314956e68fd3a7997dcc3ee190f230bd43275e8
Cr-Commit-Position: refs/heads/master@{#292951}

[Andrew Hayden (chromium.org), 2014-09-02 13:50:11]

This L*gtm, but I have almost no context here. I am surprised that
"mainThreadIsolate" isn't named "mainThreadV8Isolate" or something in WebKit.h,
but this seems procedurally sound to me.

[haraken, 2014-09-02 14:55:35]

LGTM

[jochen (gone - plz use gerrit), 2014-09-02 16:23:23]

The CQ bit was checked by jochen@chromium.org

[commit-bot: I haz the power, 2014-09-02 16:23:38]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/jochen@chromium.org/526973003/1

[commit-bot: I haz the power, 2014-09-02 17:15:07]

Committed patchset #1 (id:1) as 951da38c1b91e24ce31cc3342f5867baf3146701

[commit-bot: I haz the power, 2014-09-10 03:19:14]

Patchset 1 (id:??) landed as
https://crrev.com/1314956e68fd3a7997dcc3ee190f230bd43275e8
Cr-Commit-Position: refs/heads/master@{#292951}