Add exc_client_variants (UniversalRaiseException()) and its test

util/mach/mach_extensions.cc

Index: util/mach/mach_extensions.cc
diff --git a/util/mach/mach_extensions.cc b/util/mach/mach_extensions.cc
new file mode 100644
index 0000000000000000000000000000000000000000..865bf9b7ef150f1f9e13b9968f34d75b4d9924ed
--- /dev/null
+++ b/util/mach/mach_extensions.cc
@@ -0,0 +1,27 @@
+// Copyright 2014 The Crashpad Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "util/mach/mach_extensions.h"
+
+#include <pthread.h>
+
+namespace crashpad {
+
+mach_port_t MachThreadSelf() {
+  // The pthreads library keeps its own copy of the mach_port_t. Using it does
+  // not increment its reference count.
+  return pthread_mach_thread_np(pthread_self());
+}
+
+}  // namespace crashpad