Introduce the ability to wait for the watcher process to initialize.

chrome/app/chrome_watcher_client_win.h

+// Copyright 2015 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 CHROME_APP_CHROME_WATCHER_CLIENT_WIN_H_
+#define CHROME_APP_CHROME_WATCHER_CLIENT_WIN_H_
+
+#include <windows.h>
+
+#include "base/callback.h"
+#include "base/command_line.h"
+#include "base/macros.h"
+#include "base/process/process.h"
+#include "base/win/scoped_handle.h"
+
+namespace base {
+class TimeDelta;
+}  // namespace base
+
+// Launches a Chrome watcher process and permits the client to wait until the
+// process is fully initialized.
+class ChromeWatcherClient {
+ public:
+  // A CommandLineGenerator generates command lines that will launch a separate
+  // process and pass the supplied HANDLE values to WatcherMain in that process.
+  // The first HANDLE is an event that should be signaled when the watcher
+  // process is fully initialized. The second HANDLE is the process that the
+  // watcher process should watch.
+  // The process will be launched such that the HANDLEs are inherited by the
+  // new process.
+  typedef base::Callback<base::CommandLine(HANDLE, HANDLE)>
+      CommandLineGenerator;
+
+  // Constructs an instance that launches its watcher process using the command
+  // line generated by |command_line_generator|.
+  explicit ChromeWatcherClient(
+      const CommandLineGenerator& command_line_generator);
+
+  ~ChromeWatcherClient();
+
+  // Launches the watcher process such that the child process is able to inherit
+  // a handle to the current process. Returns true if the process is
+  // successfully launched.
+  bool LaunchWatcher();
+
+  // Blocks until the process, previously launched by LaunchWatcher, is either
+  // fully initialized or has terminated. Returns true if the process
+  // successfully initializes. May be called multiple times.
+  bool EnsureInitialized();
+
+  // Waits for the process to exit. Returns true on success. It is up to the
+  // client to somehow signal the process to exit.
+  bool WaitForExit(int* exit_code);
+
+  // Same as WaitForExit() but only waits for up to |timeout|.
+  bool WaitForExitWithTimeout(const base::TimeDelta& timeout, int* exit_code);

[grt (UTC plus 2), 2015/02/03 21:20:45]

i think TimeDelta is ordinarily passed by value (it's an int64_t).

[grt (UTC plus 2), 2015/02/04 03:04:47]

my possibly flawed codesearch for uses of base::TimeDelta in .h files with and
without & also indicates that it's generally passed by value.

[erikwright (departed), 2015/02/04 04:19:18]

Sorry, just overlooked this the first time.

+
+ private:
+  CommandLineGenerator command_line_generator_;
+  base::win::ScopedHandle on_initialized_event_;
+  base::Process process_;
+
+  DISALLOW_COPY_AND_ASSIGN(ChromeWatcherClient);
+};
+
+#endif  // CHROME_APP_CHROME_WATCHER_CLIENT_WIN_H_