DevTools: Prevent breaking program if already paused.
DevTools: Prevent breaking program if already paused.

BUG=436328
TBR=yurys

Review URL: https://codereview.chromium.org/783553002

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@186533 bbb929c8-8fbe-4397-9dbb-9b2b20218538

primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs