Sampling rate is now calculated as total number of samples divided by profiling time in ms. Before the patch the sampling rate was updated once per 100ms which doesn't have any obvious advantage over the simpler method.

Also we are going to get rid of the profile node self and total time calculation in the v8 CPU profiler and only expose profiling start/end time for CpuProfile and number of ticks on each ProfileNode and let clients do all the math should they need it.

BUG=None
R=bmeurer@chromium.org, loislo@chromium.org

Review URL: https://codereview.chromium.org/21105003

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@15944 ce2b1a6d-e550-0410-aec6-3dcde31c8c00