Disable two DomSerializerTests in preperation of page serializer merge

BUG=328354

Review URL: https://codereview.chromium.org/115163002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@240671 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 240671