Oilpan: have WebPerformance use transition types.

Also have DOMWindow keep a persistent reference to its Performance object.

R=
BUG=340522

Review URL: https://codereview.chromium.org/197283036

git-svn-id: svn://svn.chromium.org/blink/trunk@169532 bbb929c8-8fbe-4397-9dbb-9b2b20218538