Made --apps-use-native-frame flag available on Mac.

This flag has been meaningful on Mac as of r213834.

BUG=268789

Review URL: https://chromiumcodereview.appspot.com/22365002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@215857 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/about_flags.cc

@@ -1457,7 +1457,7 @@ const Experiment kExperiments[] = {
     "apps-use-native-frame",
     IDS_FLAGS_ENABLE_NATIVE_FRAMES_FOR_APPS_NAME,
     IDS_FLAGS_ENABLE_NATIVE_FRAMES_FOR_APPS_DESCRIPTION,
-    kOsWin,
+    kOsMac | kOsWin,
     SINGLE_VALUE_TYPE(switches::kAppsUseNativeFrame)
   },
   {