restore isLoadLikeEvent

fixes https://github.com/Polymer/platform/issues/83

isLoadLikeEvent is from: https://github.com/Polymer/ShadowDOM/commit/b04881f3b00925daa96b6c7256fb046d9706d499#diff-960ceb36e2dc9470f018834bd9019745L190

I wrote the test first to verify it reproduces the issue (it passes if shadowdom.js+wrap call is not there, before the fix and with shadowdom.js, it fails at the 2000ms timeout)