Use CpuProfileNode::GetHitCount instead of depreceted GetSelfSamplesCount

BUG=267595
R=pfeldman@chromium.org

Review URL: https://codereview.chromium.org/22684004

git-svn-id: svn://svn.chromium.org/blink/trunk@156096 bbb929c8-8fbe-4397-9dbb-9b2b20218538