It's important in multi-session case, each agent should cleanup own breakpoints on disabled.

R=dgozman@chromium.org

Bug: none
Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I1b2182aa01e74c7e9f36addf998c779d1d32feef
Reviewed-on: https://chromium-review.googlesource.com/594272
Commit-Queue: Aleksey Kozyatinskiy <kozyatinskiy@chromium.org>
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47103}