mac: Prepare most test code for -Wunused-functions too.

BUG=315884
R=akalin@chromium.org, isherman@chromium.org, thestig@chromium.org, yzshen@chromium.org
TBR=piman, sergeyu

Review URL: https://codereview.chromium.org/65813002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@233737 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 233737