crash-reporter: add filtering to make crash tests resilient to crashy builds

BUG=8415
TEST=Run UserCrash and CrashSender while an unrelated process is crashing at about 10Hz

Change-Id: I7f86df8caec19278337ca463f09705e4fcd788f3

Review URL: http://codereview.chromium.org/4190014
1 file changed