Clean up isolate argument in throw error.

Remove some optional isolate = 0 which are not being used.

throwError(v8::Handle<v8::Value>) does not need an isolate. So remove
param where possible.

BUG=None

Review URL: https://chromiumcodereview.appspot.com/19517004

git-svn-id: svn://svn.chromium.org/blink/trunk@154504 bbb929c8-8fbe-4397-9dbb-9b2b20218538