Fix iOS8 crash in background mode.

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

Index: webrtc/sdk/objc/Framework/Classes/UIDevice+RTCDevice.mm
diff --git a/webrtc/sdk/objc/Framework/Classes/UIDevice+RTCDevice.mm b/webrtc/sdk/objc/Framework/Classes/UIDevice+RTCDevice.mm
index 523c950645fa4ca294e183c7143bc4e81a644710..94faf53506b6e8d039a038117a7579d1a45069a4 100644
--- a/webrtc/sdk/objc/Framework/Classes/UIDevice+RTCDevice.mm
+++ b/webrtc/sdk/objc/Framework/Classes/UIDevice+RTCDevice.mm
@@ -165,4 +165,12 @@ + (NSString *)stringForDeviceType:(RTCDeviceType)deviceType {
   return @"Unknown";
 }
 
++ (double)currentDeviceSystemVersion {
+  return [self currentDevice].systemVersion.doubleValue;
+}
+
++ (BOOL)isIOS9OrLater {
+  return [self currentDeviceSystemVersion] >= 9.0;
+}
+
 @end