Transfer only self tick count for each CPU profile node

CPUProfile now contains start and end time in milliseconds and humber of samples for each node (hitCount). selfTime and totalTime are calculated based on them.

BUG=267595
R=alph@chromium.org

Review URL: https://codereview.chromium.org/21908002

git-svn-id: svn://svn.chromium.org/blink/trunk@155755 bbb929c8-8fbe-4397-9dbb-9b2b20218538