Create unprefixed versions of pointerlockchange & pointerlockerror events.

Part of unprefixing the entire pointer lock API.

LayoutTests are duplicated into new files with suffix "-prefixed"
and the originals are modified to use the new unprefixed API.

BUG=359738

Review URL: https://codereview.chromium.org/266533004

git-svn-id: svn://svn.chromium.org/blink/trunk@173427 bbb929c8-8fbe-4397-9dbb-9b2b20218538