Moving fontSelector from StyleResolver to StyleEngine.

To avoid dispatching fontLoaded event multiple times for the same font (caused by clearResolver), we should change fontSelector's owner.

BUG=236298,305885

Review URL: https://codereview.chromium.org/87503003

git-svn-id: svn://svn.chromium.org/blink/trunk@163369 bbb929c8-8fbe-4397-9dbb-9b2b20218538