notif: Use Zulip's notification sound on Android

Updates: #340

Author: rajveermalviya

android/app/src/main/res/raw/chime3.m4a

@@ -12,5 +12,5 @@
        https://github.com/zulip/zulip-flutter/issues/528
      -->
 <resources xmlns:tools="http://schemas.android.com/tools"
-    tools:keep="@drawable/zulip_notification"
+    tools:keep="@drawable/zulip_notification,@raw/chime3"
     />

android/app/src/main/res/raw/keep.xml

@@ -26,7 +26,10 @@ AndroidNotificationHostApi get _androidHost => ZulipBinding.instance.androidNoti
 /// Service for configuring our Android "notification channel".
 class NotificationChannelManager {
   @visibleForTesting
-  static const kChannelId = 'messages-1';
+  static const kChannelId = 'messages-2';
+
+  @visibleForTesting
+  static const kDefaultSoundResourceName = 'chime3'; // 'Zulip - Chime.m4a'
 
   /// The vibration pattern we set for notifications.
   // We try to set a vibration pattern that, with the phone in one's pocket,
@@ -78,8 +81,8 @@ class NotificationChannelManager {
       name: 'Messages', // TODO(i18n)
       importance: NotificationImportance.high,
       lightsEnabled: true,
+      soundResourceName: kDefaultSoundResourceName,
       vibrationPattern: kVibrationPattern,
-      // TODO(#340) sound
     ));
   }
 }

lib/notifications/display.dart

@@ -127,7 +127,7 @@ void main() {
         ..name.equals('Messages')
         ..importance.equals(NotificationImportance.high)
         ..lightsEnabled.equals(true)
-        ..soundResourceName.isNull()
+        ..soundResourceName.equals(NotificationChannelManager.kDefaultSoundResourceName)
         ..vibrationPattern.isNotNull().deepEquals(
             NotificationChannelManager.kVibrationPattern)
       ;