Add mach ports support to the Mojo shell.

mojo/shell/runner/host/mach_broker.h

Index: mojo/shell/runner/host/mach_broker.h
diff --git a/mojo/shell/runner/host/mach_broker.h b/mojo/shell/runner/host/mach_broker.h
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+++ b/mojo/shell/runner/host/mach_broker.h
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+// Copyright 2016 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 MOJO_SHELL_RUNNER_HOST_MACH_BROKER_H_
+#define MOJO_SHELL_RUNNER_HOST_MACH_BROKER_H_
+
+#include "base/mac/mach_port_broker.h"
+
+namespace base {
+template <typename T> struct DefaultSingletonTraits;
+}
+
+namespace mojo {
+namespace shell {
+
+// A global singleton |MachBroker| is used by the shell to provide access to
+// Mach task ports for shell out-of-process applications.
+class MachBroker {
+ public:
+  // Sends the task port of the current process to the parent over Mach IPC.
+  // For use in child processes.
+  static void SendTaskPortToParent();
+
+  // Returns the global |MachBroker|. For use in the shell.
+  static MachBroker* GetInstance();
+
+  // Registers |pid| with a MACH_PORT_NULL task port in the port provider. A
+  // child's pid must be registered before the broker will accept a task port
+  // from that child.
+  // Callers MUST acquire the lock given by GetLock() before calling this method
+  // (and release the lock afterwards).
+  void ExpectPid(base::ProcessHandle pid);
+
+  // Removes |pid| from the port provider.
+  // Callers MUST acquire the lock given by GetLock() before calling this method
+  // (and release the lock afterwards).
+  void RemovePid(base::ProcessHandle pid);
+
+  base::Lock& GetLock() { return broker_.GetLock(); }
+  base::PortProvider* port_provider() { return &broker_; }
+
+ private:
+  MachBroker();
+  ~MachBroker();
+  friend struct base::DefaultSingletonTraits<MachBroker>;
+
+  base::MachPortBroker broker_;
+};
+
+}  // namespace shell
+}  // namespace mojo
+
+#endif  // MOJO_SHELL_RUNNER_HOST_MACH_BROKER_H_