If a crash dialog can't be shown, just kill the process.

scheduleCrash() calls into the app process to ask it to nicely show
the crash dialog. If that call fails, rather than just silently
stopping, kill the process right away. It might be out of control.

This also adds an additional check for killedByAm to the flow there
so if the activity manager already has killed it, the dialog won't
be shown.

Bug: 28196243
Change-Id: I979f01074e5890640e7b06e29eeb0d6c38803569