Use V8ScriptRunner's method in _NPN_Enumerate
Use V8ScriptRunner's method in _NPN_Enumerate

A slight change is that the new code adds MicortaskScope around Script::Run().
This won't affect behavior.

BUG=241743
R=abarth

Review URL: https://chromiumcodereview.appspot.com/15735002

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@150927 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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