Skip ANR for processes that have been killed

If a controller is attached and decides to kill a process after an ANR,
other ANR reports for that app that are queued up won't be handled until
after the app has died.  This can create a report without the relevant
callstacks because the app is dead by the time the traces are dumped.
Since the trace file is global, the traces recorded for the first ANR
are overwritten, leaving us with no clue as to what happened.

After the app has been killedByAm, it is not interesting to handle ANRs
for that app until it is started again, so killedByAm can be used to
filter out these spurious reports.

Change-Id: I34ba790f6d29d563c819dc2f6ac71a3c8955bb76

services/core/java/com/android/server/am/AppErrors.java

@@ -753,6 +753,9 @@ class AppErrors {
             } else if (app.crashing) {
                 Slog.i(TAG, "Crashing app skipping ANR: " + app + " " + annotation);
                 return;
+            } else if (app.killedByAm) {
+                Slog.i(TAG, "App already killed by AM skipping ANR: " + app + " " + annotation);
+                return;
             }
 
             // In case we come through here for the same app before completing