DevTools: Optimize heap snapshot sorting comparator.

Major gains come from:
1. typeof is gone
2. method name lookup is hoisted out of the loop.

R=yurys@chromium.org

Review URL: https://codereview.chromium.org/196023010

git-svn-id: svn://svn.chromium.org/blink/trunk@169232 bbb929c8-8fbe-4397-9dbb-9b2b20218538