Add heap leak check suppression for flaky net_unittest.

R=machenbach@chromium.org
BUG=323149

Review URL: https://codereview.chromium.org/85653002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@237073 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 237073