Introduce use counters for Blink specific editing event usage

This patch introduces Blink specific editing events usage with |addEventListener| for
 - textInput
 - webkitBeforeTextInserted
 - webkitEditableContentChanged

We would like to deprecate these Blink specific events and replace them standard one, e.g. beforeinput, or use another way to implement editing functionality if community agreed.

The usage data collected from use counter introduced by this patch are important for decision.

BUG=382814
TEST=n/a

Review URL: https://codereview.chromium.org/328513004

git-svn-id: svn://svn.chromium.org/blink/trunk@175945 bbb929c8-8fbe-4397-9dbb-9b2b20218538