Faster event listener collection

[paulirish]

we have Two options for our remaining uses of event listener collection:

1. DOMDebugger.getEventListeners now has a pierce option (added for us) so that we dont need to ask for each individual element's listener
2. pavel was exploring reporting mutation listeners as violations: https://codereview.chromium.org/2863183003 not sure if this will land

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also separately..

scriptParsed snapshot
instead of leaving scriptParsed open for the entire run we just use it for a quick snapshot.

between the Debugger.enable command and its callback/resolution, we'll get all the scriptParsed events flushed at us. So we can instantly disable it right after it resolves.