Implements secure sockets on Mac OS with SecureTransport API

runtime/bin/secure_socket_boringssl.cc

Index: runtime/bin/secure_socket_boringssl.cc
diff --git a/runtime/bin/secure_socket.cc b/runtime/bin/secure_socket_boringssl.cc
similarity index 99%
rename from runtime/bin/secure_socket.cc
rename to runtime/bin/secure_socket_boringssl.cc
index f419c04ad8e738796161a6df88fa7cd3b6e04a40..6c4df2b66a046f8c40384c724462acf56549965e 100644
--- a/runtime/bin/secure_socket.cc
+++ b/runtime/bin/secure_socket_boringssl.cc
@@ -2,7 +2,13 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+#include "platform/globals.h"
+#if defined(TARGET_OS_ANDROID) || \
+    defined(TARGET_OS_LINUX)   || \
+    defined(TARGET_OS_WINDOWS)
+
 #include "bin/secure_socket.h"
+#include "bin/secure_socket_boringssl.h"
 
 #include <errno.h>
 #include <fcntl.h>
@@ -760,6 +766,11 @@ void FUNCTION_NAME(SecurityContext_SetTrustedCertificatesBytes)(
 }
 
 
+void FUNCTION_NAME(SecurityContext_AlpnSupported)(Dart_NativeArguments args) {
+  Dart_SetReturnValue(args, Dart_NewBoolean(true));
+}
+
+
 void FUNCTION_NAME(SecurityContext_TrustBuiltinRoots)(
     Dart_NativeArguments args) {
   SSL_CTX* context = GetSecurityContext(args);
@@ -1654,3 +1665,5 @@ int SSLFilter::ProcessWriteEncryptedBuffer(int start, int end) {
 
 }  // namespace bin
 }  // namespace dart
+
+#endif  // defined(TARGET_OS_LINUX)