video: pause in background mode

When application enter background VideoToolbox session become invalid
and need to be reset when application enter foreground. This patch
disable video when enter background and enable when entering foreground.

Change-Id: I5a307ca99298a6fb891b5b6d3920954c06e4d952

Ring/Ring/AppDelegate.swift

@@ -205,12 +205,14 @@ class AppDelegate: UIResponder, UIApplicationDelegate, UNUserNotificationCenterD
 
     func applicationDidEnterBackground(_ application: UIApplication) {
         self.log.warning("entering background")
+        self.callService.muteCurrentCallVideoVideo( mute: true)
     }
 
     func applicationWillEnterForeground(_ application: UIApplication) {
         self.log.warning("entering foreground")
         self.daemonService.connectivityChanged()
         self.updateNotificationAvailability()
+        self.callService.muteCurrentCallVideoVideo( mute: false)
     }
 
     func applicationWillTerminate(_ application: UIApplication) {

Ring/Ring/Services/CallsService.swift

@@ -206,6 +206,16 @@ class CallsService: CallsAdapterDelegate {
                        muted: mute)
     }
 
+    func muteCurrentCallVideoVideo(mute: Bool) {
+        for call in self.calls.values where call.state == .current {
+                self.callsAdapter
+                    .muteMedia(call.callId,
+                               mediaType: String(describing: MediaType.video),
+                               muted: mute)
+                return
+        }
+    }
+
     func playDTMF(code: String) {
         self.callsAdapter.playDTMF(code)
     }