Remove unused WebFontCache APIs.

Also adjust FontCache accordingly.

BUG=315783
R=eae

Review URL: https://codereview.chromium.org/81643002

git-svn-id: svn://svn.chromium.org/blink/trunk@162585 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Move BufferedLineReader into html/track/vtt.

BUG=322784

Review URL: https://codereview.chromium.org/83343005

git-svn-id: svn://svn.chromium.org/blink/trunk@162586 bbb929c8-8fbe-4397-9dbb-9b2b20218538