Fix iOS8 crash in background mode.

webrtc/sdk/objc/Framework/Classes/UIDevice+RTCDevice.mm

 /*
  *  Copyright 2016 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 147 matching lines @@
     case RTCDeviceTypeIPadMini2GCellular:
       return @"iPad Mini 2G (Cellular)";
     case RTCDeviceTypeSimulatori386:
       return @"i386 Simulator";
     case RTCDeviceTypeSimulatorx86_64:
       return @"x86_64 Simulator";
   }
   return @"Unknown";
 }
 
++ (double)currentDeviceSystemVersion {
+  return [self currentDevice].systemVersion.doubleValue;
+}
+
++ (BOOL)isIOS9OrLater {
+  return [self currentDeviceSystemVersion] >= 9.0;
+}
+
 @end