Fix VideoToolbox backgrounding issues

webrtc/base/objc/RTCUIApplication.mm

Index: webrtc/base/objc/RTCUIApplication.mm
diff --git a/webrtc/base/objc/RTCMacros.h b/webrtc/base/objc/RTCUIApplication.mm
similarity index 59%
copy from webrtc/base/objc/RTCMacros.h
copy to webrtc/base/objc/RTCUIApplication.mm
index 9d4646bd2187cfd6990677ae77037bd7b6754a53..85376b4e0e7fe914e924cff28fc7d03c5a04c87f 100644
--- a/webrtc/base/objc/RTCMacros.h
+++ b/webrtc/base/objc/RTCUIApplication.mm
@@ -8,8 +8,15 @@
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
-#if defined(__cplusplus)
-  #define RTC_EXPORT extern "C"
-#else
-  #define RTC_EXPORT extern
-#endif
+#include "webrtc/base/objc/RTCUIApplication.h"
+
+#if defined(WEBRTC_IOS)
+
+#import <UIKit/UIKit.h>
+
+bool RTCIsUIApplicationActive() {
+  UIApplicationState state = [UIApplication sharedApplication].applicationState;
+  return state == UIApplicationStateActive;
+}
+
+#endif // WEBRTC_IOS