Manage FileSystem callbacks with OwnPtr instead of refcounting

Most changes were mechanical, with the only tricky bit being in
DOMFileSystemSync::createWriter, where some code was refactored and some
ASSERTs were removed (hopefully it's safe to leave those ASSERTs out).

Also remove the ability of the code generator to create refcounted callbacks,
as modules/filesystem/ was the last codebase relying on refcounting.

BUG=323681

Review URL: https://codereview.chromium.org/105523002

git-svn-id: svn://svn.chromium.org/blink/trunk@163234 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Web Animations: Use Infinity instead of NaN in timeToNextIteration

BUG=325713

Review URL: https://codereview.chromium.org/105883002

git-svn-id: svn://svn.chromium.org/blink/trunk@163235 bbb929c8-8fbe-4397-9dbb-9b2b20218538