[mojo] Use a pipe path to initialise Mojo in elevated utility processes.

mojo/edk/embedder/named_platform_channel_pair.h

+// 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_EDK_EMBEDDER_NAMED_PLATFORM_CHANNEL_PAIR_H_
+#define MOJO_EDK_EMBEDDER_NAMED_PLATFORM_CHANNEL_PAIR_H_
+
+#include <string>
+
+#include "base/macros.h"
+#include "base/strings/string16.h"
+#include "build/build_config.h"
+#include "mojo/edk/embedder/scoped_platform_handle.h"
+#include "mojo/edk/system/system_impl_export.h"
+
+namespace base {
+class CommandLine;
+}
+
+namespace mojo {
+namespace edk {
+
+// This is used to create a named bidirectional pipe to connect new child
+// processes. The resulting server handle should be passed to the EDK, and the
+// child end passed as a pipe name on the command line to the child process. The
+// child process can then retrieve the pipe name from the command line and
+// resolve it into a client handle.
+class MOJO_SYSTEM_IMPL_EXPORT NamedPlatformChannelPair {
+ public:
+  NamedPlatformChannelPair();
+  ~NamedPlatformChannelPair();
+
+  // Note: It is NOT acceptable to use this handle as a generic pipe channel. It
+  // MUST be passed to mojo::edk::ChildProcessLaunched() only.
+  ScopedPlatformHandle PassServerHandle();
+
+  // To be called in the child process, after the parent process called
+  // |PrepareToPassClientHandleToChildProcess()| and launched the child (using
+  // the provided data), to create a client handle connected to the server
+  // handle (in the parent process).
+  static ScopedPlatformHandle PassClientHandleFromParentProcess(
+      const base::CommandLine& command_line);
+
+  // Prepares to pass the client channel to a new child process, to be launched
+  // using |LaunchProcess()| (from base/launch.h). Modifies |*command_line| and
+  // |*handle_passing_info| as needed.
+  // Note: For Windows, this method only works on Vista and later.
+  void PrepareToPassClientHandleToChildProcess(
+      base::CommandLine* command_line) const;
+
+ private:
+  ScopedPlatformHandle server_handle_;
+
+#if defined(OS_WIN)
+  base::string16 pipe_name_;
+#endif
+
+  DISALLOW_COPY_AND_ASSIGN(NamedPlatformChannelPair);
+};
+
+}  // namespace edk
+}  // namespace mojo
+
+#endif  // MOJO_EDK_EMBEDDER_NAMED_PLATFORM_CHANNEL_PAIR_H_