[content shell] protect against the case when a RPH dies before the process launched

e.g.
http/tests/xmlhttprequest/access-control-repeated-failed-preflight-crash.html
quickly opens and closes the devtools. If a new RPH is then created and happens
to be at the same location, we'll register twice for the process created
notification.

BUG=111316
R=marja@chromium.org

Review URL: https://chromiumcodereview.appspot.com/16023012

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@202465 0039d316-1c4b-4281-b951-d872f2087c98
1 file changed