Make sure CPU profiler collects a sample on start.

BUG=369035
LOG=N
R=bmeurer@chromium.org, yurys@chromium.org

Review URL: https://codereview.chromium.org/263883008

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21157 ce2b1a6d-e550-0410-aec6-3dcde31c8c00