DevTools: Improve performance of the element breadcrumbs.

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

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=156551

Review URL: https://chromiumcodereview.appspot.com/22548006

git-svn-id: svn://svn.chromium.org/blink/trunk@156560 bbb929c8-8fbe-4397-9dbb-9b2b20218538