Pass AtomicStrings as 2 first arguments to V8LazyEventListener::create()

Pass AtomicStrings as 2 first arguments to V8LazyEventListener::create() in
ScriptEventListener as this is what this factory method expects. This avoids
uselessly constructing Strings and then converting them to AtomicStrings.

R=abarth
BUG=323739

Review URL: https://codereview.chromium.org/89993002

git-svn-id: svn://svn.chromium.org/blink/trunk@162718 bbb929c8-8fbe-4397-9dbb-9b2b20218538