dom-ui settings: Show Mac address book checkbox.

BUG=64800
TEST=Verify that the checkbox for the Mac address book appears in autofill options.
Review URL: http://codereview.chromium.org/6278012

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@72089 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/resources/options/autofill_options.html

 <div id="autofill-options" class="page hidden">
   <h1 i18n-content="autoFillOptionsTitle"></h1>
-<if expr="pp_ifdef('darwin')">
+<if expr="os == 'darwin'">
   <label class="checkbox">
     <input pref="autofill.auxiliary_profiles_enabled" type="checkbox">
     <span i18n-content="auxiliaryProfilesEnabled"></span>