Remove OVERRIDEs from WebSourceBufferImpl
Removes OVERRIDEs for this Chromium implementation of a Blink interface.
Discussion revealed this is allowed (and preferred), to reduce cross-repo API change difficulties.
Also removes TODOs related to some pending OVERRIDE additions (see the referenced bugs). Though the Blink changes have landed, OVERRIDE is undesired.
R=acolwell@chromium.org
BUG=166465,229408
Review URL: https://codereview.chromium.org/
123483002
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@242912 0039d316-1c4b-4281-b951-d872f2087c98