Protect RDFa attributes from obliteration

Firefox decides to not keep some attributes when copying, so JSON
encode them in a data attribute.

Bug: 59145
Bug: 59154
Bug: 59170
Bug: 59171
Bug: 59173
Change-Id: Iae87a6e145d92eb98f46367318230c4c6fc2f4ed
Merge "Protect RDFa attributes from obliteration"