Notification importance/selected sound conflict fixes.

- When you've selected "Silent" as your sound, update notification
importance messaging to match.
- When you explicitly move from a silent type of notifications to a
loud type, but have "Silent" selected as the sound, change the
sound to the default notification sound also.

Change-Id: I462785d593e1d6c7d1e87388aeee1bdcbcf6aa3d
Fixes: 63109928
Test: RunSettingsRoboTests, manual

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

@@ -46,6 +46,7 @@ import android.content.pm.PackageManager;
 import android.content.pm.PackageManager.NameNotFoundException;
 import android.content.pm.ResolveInfo;
 import android.content.pm.UserInfo;
+import android.net.Uri;
 import android.os.Bundle;
 import android.os.UserHandle;
 import android.os.UserManager;
@@ -506,4 +507,8 @@ abstract public class NotificationSettingsBase extends SettingsPreferenceFragmen
             }
         }
     };
+
+    boolean hasValidSound(NotificationChannel channel) {
+        return channel.getSound() != null && !Uri.EMPTY.equals(channel.getSound());
+    }
 }