Migrate from using URLs to Entries in the Files app's video player.

This patch converts urls as soon as possible to file entries, in the initialization stage, so later only entries are used.

TEST=Tested manually.
BUG=327592
R=yoshiki@chromium.org

Review URL: https://codereview.chromium.org/110693003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@240538 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 240538