Store alien meta items' dom nodes only

We don't need to decompose and rebuild alien meta items
as they are uneditable, so just store the dom node and return that
in toDomElements.

Update test cases and several tests now need to use
assert.deepEqualWithDomElements.

Change-Id: I4d2eed267dac7855cb929a17d7aef566eaf0e287
Merge "Store alien meta items' dom nodes only"