Cleanup conditionals in L10nUtilTest.GetAppLocale

This test is pretty hard to understand. Replace most of the idefs with
constants that describe the expected behavior of GetApplicationLocale for
the platform. No functional change.

Review URL: https://codereview.chromium.org/80823004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@236700 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 236700