Don't crash apps unfairly under FAS

When an app calls startForegroundService() from a bg state (e.g. from a
broadcast receiver) but the user has placed it under FAS, it's incorrect
to crash the app:  it hasn't actually violated the fg/bg restrictions
contract.  Fail quietly instead, just like the legacy-app case when O+
restrictions are imposed on it.

Change-Id: I3e8ed2ea6bdbf4167249132ddf9b7c549b9a8062
Fixes: 79235311
Test: ApiDemos [before and after changing target sdk to O+]
Test: atest android.app.cts.ServiceTest

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

@@ -476,12 +476,23 @@ public final class ActiveServices {
                 Slog.w(TAG, "Background start not allowed: service "
                         + service + " to " + r.name.flattenToShortString()
                         + " from pid=" + callingPid + " uid=" + callingUid
-                        + " pkg=" + callingPackage);
+                        + " pkg=" + callingPackage + " startFg?=" + fgRequired);
                 if (allowed == ActivityManager.APP_START_MODE_DELAYED || forceSilentAbort) {
                     // In this case we are silently disabling the app, to disrupt as
                     // little as possible existing apps.
                     return null;
                 }
+                if (forcedStandby) {
+                    // This is an O+ app, but we might be here because the user has placed
+                    // it under strict background restrictions.  Don't punish the app if it's
+                    // trying to do the right thing but we're denying it for that reason.
+                    if (fgRequired) {
+                        if (DEBUG_BACKGROUND_CHECK) {
+                            Slog.v(TAG, "Silently dropping foreground service launch due to FAS");
+                        }
+                        return null;
+                    }
+                }
                 // This app knows it is in the new model where this operation is not
                 // allowed, so tell it what has happened.
                 UidRecord uidRec = mAm.mActiveUids.get(r.appInfo.uid);