StopCpuProfiling is replaced with StopProfiling which returns non-const CpuProfile which allows to call CpuProfile::Delete on it without const_cast. Also replaced StartCpuProfiling with StartProfiling to have symmetric names for start/stop actions.

BUG=v8:3213
LOG=Y
R=alph@chromium.org, svenpanne@chromium.org

Review URL: https://codereview.chromium.org/197873015

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@19918 ce2b1a6d-e550-0410-aec6-3dcde31c8c00