Bug 918806 - Enable DOM Promises. sr=bz

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extra : rebase_source : dbc7ef836fe7c2a71f38fedda004d7f988361a85
Bug 918806 - Remove all mention of dom.promise.enabled from other tests. r=bz,schien

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extra : rebase_source : a07485081313d6002459bd64e3abf4ebb10b960d
Bug 918806 - Add Promise to test_interfaces.html on all builds. r=bz

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extra : rebase_source : dc56e8959919796783698b15864c88a27e49dbfc