GTTF: Make test launcher unset GTEST_ env variables since it handles all of sharding.

This is a relanding of https://codereview.chromium.org/60983004/ which checks
for variable existence before unsetting to avoid failing on Windows XP.

BUG=236893
R=kbr@chromium.org

Review URL: https://codereview.chromium.org/67183003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@233960 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 233960
Fix cookies not being set with NPAPI plugin request.

BUG=316511
R=ananta@chromium.org

Review URL: https://codereview.chromium.org/66663003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@233961 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 233961