DevTools: Improve performance of the element breadcrumbs.

BUG=237447,269067
R=pfeldman@chromium.org

Review URL: https://codereview.chromium.org/22548006

git-svn-id: svn://svn.chromium.org/blink/trunk@156551 bbb929c8-8fbe-4397-9dbb-9b2b20218538