Adds support for Bluetooth headsets to the iOS audio layer

webrtc/modules/utility/source/helpers_ios.mm

Index: webrtc/modules/utility/source/helpers_ios.mm
diff --git a/webrtc/modules/utility/source/helpers_ios.mm b/webrtc/modules/utility/source/helpers_ios.mm
index d36253072d71b45dcb9601c4ff3f4ebb4d9b4546..cca4c11fbb40ea8480ec1544991d8aff51deafb5 100644
--- a/webrtc/modules/utility/source/helpers_ios.mm
+++ b/webrtc/modules/utility/source/helpers_ios.mm
@@ -10,6 +10,7 @@
 
 #if defined(WEBRTC_IOS)
 
+#import <AVFoundation/AVFoundation.h>
 #import <Foundation/Foundation.h>
 #import <sys/sysctl.h>
 #import <UIKit/UIKit.h>
@@ -57,6 +58,11 @@ std::string GetCurrentThreadDescription() {
   return StdStringFromNSString(name);
 }
 
+std::string GetAudioSessionCategory() {
+  NSString* category = [[AVAudioSession sharedInstance] category];
+  return StdStringFromNSString(category);
+}
+
 std::string GetSystemName() {
   NSString* osName = [[UIDevice currentDevice] systemName];
   return StdStringFromNSString(osName);