Revert of Do not initialize v8::Context on |ScriptController::updateDocument|.

Revert of Do not initialize v8::Context on |ScriptController::updateDocument|. (https://codereview.chromium.org/263583002/)

Reason for revert:
broke interactive_ui_tests:

Referrer
SearchReusesInstantTab
TypedSearchURLDoesntReuseInstantTab

Original issue's description:
> Do not initialize |v8::Context| on |ScriptController::updateDocument|.
> 
> Initializing |v8::Context| is a heavy operation, and should be avoided if necessary. This is meant to be delayed until first time |toV8Context| is called, but |ScriptController::updateDocument| was forcing creation.
> 
> This patch fixes the if branch so that it would not create a |v8::Context| if it does not exist.
> 
> BUG=368548, 368555
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=173044

TBR=haraken@chromium.org,jochen@chromium.org,dcarney@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=368548, 368555
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=173060

[kouhei (in TOK), 2014-05-01 04:22:02]

Created Revert of Do not initialize v8::Context on
|ScriptController::updateDocument|.

[commit-bot: I haz the power, 2014-05-01 04:22:20]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/kouhei@chromium.org/268623003/1

[haraken, 2014-05-01 04:22:34]

LGTM

[commit-bot: I haz the power, 2014-05-01 04:22:58]

Change committed as 173060