Make Pointer Lock events no longer bubble.

Specification has changed such that pointerlockchange and pointerlockerror
no longer bubble.
http://dvcs.w3.org/hg/pointerlock/raw-file/default/index.html

BUG=237169

Review URL: https://codereview.chromium.org/26237003

git-svn-id: svn://svn.chromium.org/blink/trunk@159245 bbb929c8-8fbe-4397-9dbb-9b2b20218538