GitLab

Remove PrerenderTracker::TryCancel* methods and associated ones, since destruction of prerender only happens on the UI thread through PrerenderContents now.

BUG=304341
R=mmenke@chromium.org, tburkard@chromium.org

Review URL: https://codereview.chromium.org/132613002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@244196 0039d316-1c4b-4281-b951-d872f2087c98