DevTools: limit number of crumbs strip layouts during the update to 3.

R=aandrey@chromium.org, apavlov@chromium.org

Review URL: https://codereview.chromium.org/208843006

git-svn-id: svn://svn.chromium.org/blink/trunk@169943 bbb929c8-8fbe-4397-9dbb-9b2b20218538