Unflake and speedup JsNative*Sample cpu profile tests

Instead of running cpu profiler for a hundred milliseconds,
collecting samples distributed in a non-deterministic way all along
the code, make the tests rely on a single sample we collect on
the profiler start.

R=bmeurer@chromium.org, yurys@chromium.org

Review URL: https://codereview.chromium.org/301603005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22345 ce2b1a6d-e550-0410-aec6-3dcde31c8c00