It appears that http://trac.webkit.org/changeset/112864 has broken this test on Mac. Do we need new test results?
Sorry for missing this - this test should be disabled on all platforms but Chromium (it is the only platform to implement the feature at the moment.) The bug to track the implementation of the device metrics override on other platforms is https://bugs.webkit.org/show_bug.cgi?id=82886. This test would pass previously because it had a different implementation (in WebCore). The new implementation demands certain pieces implemented in Source/WebKit/platform for every platform.
http://trac.webkit.org/changeset/112998 suppresses the test in LayoutTests/mac/Skipped