Adjust google_toolbox_for_mac.gyp to meet the needs of iOS.

TBR=darin

Review URL: https://codereview.chromium.org/149433003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247728 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 247728