Ignore first crash dialog.

By default, no longer show the crash dialog the first time an app
crashes. Instead, only multiple crashes will show by default.

Add developer setting to control behavior, so app developers can
ensure dialog always shows when a crash happens.

Bug: 63703353, 70640329
Test: robotests, manual crashing with a test app
Change-Id: I2e625ed147dafc188b28c52eb1b9cee6b2330d50