[Mac] Resolve trybot flakiness: DCHECK fail when deleting GL shader programs.

The code has other protections to ensure all programs will be eventually deleted, and only once for each time they're created.

BUG=326328
R=hclam@chromium.org

Review URL: https://codereview.chromium.org/123613005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@243196 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 243196