style: Implement offset-rotate.

This includes style system and layout update. I add 3 extra reftests
because the original tests use ray() function as the offset-path, but we
don't support it. It'd be better to add tests using a different type of
offset-path.

The spec issue about the serialization:
https://github.com/w3c/fxtf-drafts/issues/340

Differential Revision: https://phabricator.services.mozilla.com/D32212

components/style/properties/data.py

@@ -332,6 +332,7 @@ class Longhand(object):
                 "MozScriptMinSize",
                 "MozScriptSizeMultiplier",
                 "NonNegativeNumber",
+                "OffsetRotate",
                 "Opacity",
                 "OutlineStyle",
                 "Overflow",