TinyMCE wpView sandbox iframes: 
- Make them transparent.
- Don't load tons of unrelated styles that can break them. This could result in minimal styling mismatch to the front-end, but keeps the views working well and looking good.
Props avryl, fixes #29048.
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git-svn-id: http://core.svn.wordpress.org/trunk@29319 1a063a9b-81f0-0310-95a4-ce76da25c4cd