Create settings screen for Notification Assistant

Test: this atest
Test: manual: change assistant and "adb shell dumpsys notification"
Test: manual: verify persistance through reboot (including none)

Fixes:120852765
Change-Id: Ie4516c3339246d66d7b6719ac5dd1d65c4d03b57

src/com/android/settings/notification/NotificationBackend.java

@@ -23,6 +23,7 @@ import android.app.NotificationChannel;
 import android.app.NotificationChannelGroup;
 import android.app.usage.IUsageStatsManager;
 import android.app.usage.UsageEvents;
+import android.content.ComponentName;
 import android.content.Context;
 import android.content.Intent;
 import android.content.pm.ApplicationInfo;
@@ -410,6 +411,29 @@ public class NotificationBackend {
         }
     }
 
+    public ComponentName getAllowedNotificationAssistant() {
+        try {
+            return sINM.getAllowedNotificationAssistant();
+        } catch (Exception e) {
+            Log.w(TAG, "Error calling NoMan", e);
+            return null;
+        }
+    }
+
+    public boolean setNotificationAssistantGranted(ComponentName cn) {
+        try {
+            sINM.setNotificationAssistantAccessGranted(cn, true);
+            if (cn == null) {
+                return sINM.getAllowedNotificationAssistant() == null;
+            } else {
+                return cn.equals(sINM.getAllowedNotificationAssistant());
+            }
+        } catch (Exception e) {
+            Log.w(TAG, "Error calling NoMan", e);
+            return false;
+        }
+    }
+
     /**
      * NotificationsSentState contains how often an app sends notifications and how recently it sent
      * one.