Add ScopedTaskSuspend and its test

util/mach/scoped_task_suspend.h

Index: util/mach/scoped_task_suspend.h
diff --git a/util/mach/scoped_task_suspend.h b/util/mach/scoped_task_suspend.h
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+// 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.
+
+#ifndef CRASHPAD_UTIL_MACH_SCOPED_TASK_SUSPEND_H_
+#define CRASHPAD_UTIL_MACH_SCOPED_TASK_SUSPEND_H_
+
+#include <mach/mach.h>
+
+#include "base/basictypes.h"
+
+namespace crashpad {
+
+//! \brief Manages the suspension of another task.
+//!
+//! While an object of this class exists, the other task will be suspended. Once
+//! the object is destroyed, the other task will become eligible for resumption.
+//! Note that suspensions are counted, and the task will not actually resume
+//! unless its suspend count drops to 0.
+//!
+//! Callers should not attempt to suspend the current task (`mach_task_self()`).
+class ScopedTaskSuspend {
+ public:
+  explicit ScopedTaskSuspend(task_t task);
+  ~ScopedTaskSuspend();
+
+ private:
+  task_t task_;
+
+  DISALLOW_COPY_AND_ASSIGN(ScopedTaskSuspend);
+};
+
+}  // namespace crashpad
+
+#endif  // CRASHPAD_UTIL_MACH_SCOPED_TASK_SUSPEND_H_