Implements secure sockets on Mac OS with SecureTransport API

runtime/bin/secure_socket_patch.dart

Index: runtime/bin/secure_socket_patch.dart
diff --git a/runtime/bin/secure_socket_patch.dart b/runtime/bin/secure_socket_patch.dart
index 455b132db155a940eea31dd37cfab002c33125ef..c47c9415db88ebb3bada081bd0f1b96c011e3a44 100644
--- a/runtime/bin/secure_socket_patch.dart
+++ b/runtime/bin/secure_socket_patch.dart
@@ -123,6 +123,10 @@ patch class SecurityContext {
   /* patch */ static SecurityContext get defaultContext {
     return _SecurityContext.defaultContext;
   }
+
+  /* patch */ static bool get alpnSupported {
+    return _SecurityContext.alpnSupported;
+  }
 }
 
 class _SecurityContext
@@ -165,6 +169,8 @@ class _SecurityContext
   void setClientAuthoritiesBytes(List<int> authCertBytes, {String password})
       native "SecurityContext_SetClientAuthoritiesBytes";
 
+  static bool get alpnSupported => _alpnSupported();
+  static bool _alpnSupported() native "SecurityContext_AlpnSupported";
   void setAlpnProtocols(List<String> protocols, bool isServer) {
     Uint8List encodedProtocols =
         SecurityContext._protocolsToLengthEncoding(protocols);