Update from https://crrev.com/329939

base/mac/dispatch_source_mach.h

Index: base/mac/dispatch_source_mach.h
diff --git a/base/mac/dispatch_source_mach.h b/base/mac/dispatch_source_mach.h
new file mode 100644
index 0000000000000000000000000000000000000000..e7d5cb2fbb484da3616c6ab0b91b5eafe380869f
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+++ b/base/mac/dispatch_source_mach.h
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+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef BASE_MAC_DISPATCH_SOURCE_MACH_H_
+#define BASE_MAC_DISPATCH_SOURCE_MACH_H_
+
+#include <dispatch/dispatch.h>
+
+#include "base/base_export.h"
+#include "base/macros.h"
+
+namespace base {
+
+// This class encapsulates a MACH_RECV dispatch source. When this object is
+// destroyed, the source will be cancelled and it will wait for the source
+// to stop executing work. The source can run on either a user-supplied queue,
+// or it can create its own for the source.
+class BASE_EXPORT DispatchSourceMach {
+ public:
+  // Creates a new dispatch source for the |port| and schedules it on a new
+  // queue that will be created with |name|. When a Mach message is received,
+  // the |event_handler| will be called.
+  DispatchSourceMach(const char* name,
+                     mach_port_t port,
+                     void (^event_handler)());
+
+  // Creates a new dispatch source with the same semantics as above, but rather
+  // than creating a new queue, it schedules the source on |queue|.
+  DispatchSourceMach(dispatch_queue_t queue,
+                     mach_port_t port,
+                     void (^event_handler)());
+
+  // Cancels the source and waits for it to become fully cancelled before
+  // releasing the source.
+  ~DispatchSourceMach();
+
+  // Resumes the source. This must be called before any Mach messages will
+  // be received.
+  void Resume();
+
+ private:
+  // Cancels the source, after which this class will no longer receive Mach
+  // messages. Calling this more than once is a no-op.
+  void Cancel();
+
+  // The dispatch queue used to service the source_.
+  dispatch_queue_t queue_;
+
+  // A MACH_RECV dispatch source.
+  dispatch_source_t source_;
+
+  // Semaphore used to wait on the |source_|'s cancellation in the destructor.
+  dispatch_semaphore_t source_canceled_;
+
+  DISALLOW_COPY_AND_ASSIGN(DispatchSourceMach);
+};
+
+}  // namespace base
+
+#endif  // BASE_MAC_DISPATCH_SOURCE_MACH_H_