Add Metal video view in AppRTCMobile and metal availability macro.

webrtc/sdk/objc/Framework/Headers/WebRTC/RTCMTLVideoView.h

Index: webrtc/sdk/objc/Framework/Headers/WebRTC/RTCMTLVideoView.h
diff --git a/webrtc/sdk/objc/Framework/Headers/WebRTC/RTCMTLVideoView.h b/webrtc/sdk/objc/Framework/Headers/WebRTC/RTCMTLVideoView.h
index 681c457516fdf040770904207659cb55be46ba0d..859ac6de35b9d958a946a8a8b13c82ca8a279354 100644
--- a/webrtc/sdk/objc/Framework/Headers/WebRTC/RTCMTLVideoView.h
+++ b/webrtc/sdk/objc/Framework/Headers/WebRTC/RTCMTLVideoView.h
@@ -12,8 +12,15 @@
 
 #import "WebRTC/RTCVideoRenderer.h"
 
+// Check if metal is supported in WebRTC.
+// NOTE: Currently __arm64__ == Metal.
+#if defined(__arm64__) && __arm64__
+  #define RTC_SUPPORTS_METAL 1

[magjed_webrtc, 2017/02/28 17:28:15]

Don't indent and just do:
#if defined(__arm64__) && __arm64__
#define RTC_SUPPORTS_METAL
#endif
and then:
#if defined(RTC_SUPPORTS_METAL)

[daniela-webrtc, 2017/03/01 13:40:22]

Done.

+#else
+  #define RTC_SUPPORTS_METAL 0
+#endif
+
 NS_ASSUME_NONNULL_BEGIN
-RTC_EXPORT
 
 /**
  * RTCMTLVideoView is thin wrapper around MTKView.
@@ -22,6 +29,8 @@ RTC_EXPORT
  * bounds using Metal.
  */
 NS_CLASS_AVAILABLE_IOS(9)
+
+RTC_EXPORT
 @interface RTCMTLVideoView : UIView <RTCVideoRenderer>
 
 @end