Remove hidden value tracking of event listeners.

It duplicates work done by wrapper tracing. This change:
- reduces time spent in a microbenchmark of add/removeEventListener
  by 30% (approximately, measured on Linux)
- simplifies code (including removing some custom callback epilogues)
- avoids the need for an additional internal field on EventTarget
  (other than Node) wrappers

Change-Id: I06023a6bb01ac54bb9e514def17c0aaf4ae50bf0
Reviewed-on: https://chromium-review.googlesource.com/576472
Commit-Queue: Jeremy Roman <jbroman@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#491479}
49 files changed