Build cleanup following r21126. Marking Native* methods in object-observe.js as knownProblems in fuzz-natives

TBR=verwaest

Review URL: https://codereview.chromium.org/265883009

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21127 ce2b1a6d-e550-0410-aec6-3dcde31c8c00