[V8] Remove if(isolate) checks from v8String() and v8Integer()
https://bugs.webkit.org/show_bug.cgi?id=107540

Reviewed by Adam Barth.

Now there is no optional Isolate parameter in the code base
(except for throwError()). We can safely remove if(isolate) checks
from v8String() and v8Integer().

div.id:       17.8 ns => 17.8 ns (no performance change)
div.nodeType:  9.7 ns =>  8.9 ns (+8.9% performance improvement)

No tests. No change in behavior.

* bindings/v8/ScriptDebugServer.cpp:
(WebCore::ScriptDebugServer::handleV8DebugEvent):
* bindings/v8/V8Binding.h:
(WebCore::v8String):
(WebCore::v8Integer):
* bindings/v8/V8WindowErrorHandler.cpp:
(WebCore::V8WindowErrorHandler::callListenerFunction):
* bindings/v8/V8WorkerContextErrorHandler.cpp:
(WebCore::V8WorkerContextErrorHandler::callListenerFunction):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@140521 268f45cc-cd09-0410-ab3c-d52691b4dbfc