Fixes forgotten rename of -XdisplayNameMode SDM parameter

Change-Id: Ib6bb8a8f0558059b813650beee055b845262a10a
Fix bug with external at-rule using a prefix.

Fix a bug where style classes that match a external prefix and
that aren't associated to a method of the CssResource interface
were considered as non external.

Bug: issue 8960
Change-Id: Idc58856831c892ec13a011cc2eb0037236c2ae7e