Hash sink IDs with a resettable salt.

      BUG=298158

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=244944
Reverted in r244944 for test failures I can't figure out.
Relanding to see if test failures reoccur.

Review URL: https://codereview.chromium.org/111703002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@248104 0039d316-1c4b-4281-b951-d872f2087c98