Make object-observe test case resilient against GC stress.

R=rossberg@chromium.org
TEST=cctest/test-object-observe/ObservationWeakMap

Review URL: https://codereview.chromium.org/12217017

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@13597 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Add separate flag for --trace-stub-failures

R=svenpanne@chromium.org

Review URL: https://codereview.chromium.org/12208011

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@13598 ce2b1a6d-e550-0410-aec6-3dcde31c8c00