Revert "Move innerHTML and outerHTML to Element"

This reverts commit 160869 as it broke ActivityLogApiTest.TriggerEvent browser test:
http://test-results.appspot.com/dashboards/flakiness_dashboard.html#group=%40ToT%20Blink&testType=browser_tests&tests=ActivityLogApiTest.TriggerEvent

I'm not sure how severe the problem is so I'd rather revert the offending change than disable the test on Blink roll.

BUG=311080
TBR=davve@opera.com

Review URL: https://codereview.chromium.org/52203002

git-svn-id: svn://svn.chromium.org/blink/trunk@160914 bbb929c8-8fbe-4397-9dbb-9b2b20218538