[cssom-view] Editorial: mark the newly added features at risk

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extra : rebase_source : 208ae15f32db4beb62eca9e52dd11720099c5f30
[cssom-view] Make DOMRect not inherit from DOMQuad. http://lists.w3.org/Archives/Public/www-style/2013Sep/0630.html

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extra : rebase_source : 799c44c0825c47fc24272bf428d314ffd6737f54
[cssom-view] Make DOMRect mutable except for the DOMQuad#bounds one. http://lists.w3.org/Archives/Public/www-style/2013Sep/0616.html

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extra : rebase_source : d1f51745b28057052ae467bf424807b3bdff9e9b