Use RTCAudioSessionDelegate in AudioDeviceIOS.

webrtc/modules/audio_device/ios/objc/RTCAudioSessionDelegateAdapter.h

Index: webrtc/modules/audio_device/ios/objc/RTCAudioSessionDelegateAdapter.h
diff --git a/webrtc/modules/audio_device/ios/objc/RTCAudioSession+Private.h b/webrtc/modules/audio_device/ios/objc/RTCAudioSessionDelegateAdapter.h
similarity index 50%
copy from webrtc/modules/audio_device/ios/objc/RTCAudioSession+Private.h
copy to webrtc/modules/audio_device/ios/objc/RTCAudioSessionDelegateAdapter.h
index cc92ba7742422e8407ab2ef970b60cfd896fe831..0140aa043ac3e55843f01b04932ee139c341e151 100644
--- a/webrtc/modules/audio_device/ios/objc/RTCAudioSession+Private.h
+++ b/webrtc/modules/audio_device/ios/objc/RTCAudioSessionDelegateAdapter.h
@@ -10,20 +10,21 @@
 
 #import "webrtc/modules/audio_device/ios/objc/RTCAudioSession.h"
 
-NS_ASSUME_NONNULL_BEGIN
+namespace webrtc {
+class AudioSessionObserver;
+}
 
-@interface RTCAudioSession ()
+/** Adapter that forwards RTCAudioSessionDelegate calls to the appropriate
+ *  methods on the AudioSessionObserver.
+ */
+@interface RTCAudioSessionDelegateAdapter : NSObject <RTCAudioSessionDelegate>
 
-/** The delegates. */
-@property(nonatomic, readonly) NSSet *delegates;
+- (instancetype)init NS_UNAVAILABLE;
 
-/** Number of times setActive:YES has succeeded without a balanced call to
- *  setActive:NO.
+/** |observer| is a raw pointer and should be kept alive
+ *  for this object's lifetime.
  */
-@property(nonatomic, readonly) NSInteger activationCount;
-
-- (BOOL)checkLock:(NSError **)outError;
+- (instancetype)initWithObserver:(webrtc::AudioSessionObserver *)observer
+    NS_DESIGNATED_INITIALIZER;
 
 @end
-
-NS_ASSUME_NONNULL_END