Fix some html tests status that now pass on win-ff but still fail on

Fix some html tests status that now pass on win-ff but still fail on
linux-ff because apparently linux-ff buildbot runs ff13

failues in logs:
http://build.chromium.org/p/client.dart/builders/web-ff-win7/builds/3994/steps/failures%20%282012-07-30%2003%3A07%3A50.568%29/logs/stdio

Committed: https://code.google.com/p/dart/source/detail?r=10009

[Anton Muhin, 2012-07-30 11:08:09]

lgtm