Add failing test expectations for two canvas tests on Mac Lion
since they have been failing as far as we could tell on the flakiness dashboard.

The failure is tracked by the bug 105999.

* platform/mac/TestExpectations:


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@138702 268f45cc-cd09-0410-ab3c-d52691b4dbfc