Allow configuring CPU profiler sampling interval

Added a setting for selecting higher sampling rate for CPU profiler 0.1ms sampling interval vs. default 1ms one.

BUG=v8:2814
R=loislo@chromium.org

Review URL: https://codereview.chromium.org/23444035

git-svn-id: svn://svn.chromium.org/blink/trunk@157301 bbb929c8-8fbe-4397-9dbb-9b2b20218538