Revert of Roll Clang 216630:217949 (patchset #5 id:80001 of https://codereview.chromi...

Revert of Roll Clang 216630:217949 (patchset #5 id:80001 of https://codereview.chromium.org/587433002/)

Reason for revert:
Reverting due to http://crbug.com/418234. Clang was branching on undefined values.

Original issue's description:
> Roll Clang 216630:217949
>
> Also make the script revert local changes before 'svn co'
> rather than afterwards to avoid merge conflicts if a previously
> patched file changes upstream.
>
> BUG=410810
>
> Committed: https://crrev.com/ba4cf8bb6dc77ea033fe13989eb604d6069daa97
> Cr-Commit-Position: refs/heads/master@{#296870}

TBR=thakis@chromium.org,brettw@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=410810

Review URL: https://codereview.chromium.org/614453002

Cr-Commit-Position: refs/heads/master@{#297073}