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

chrome/app/chrome_watcher_command_line_win.h

Index: chrome/app/chrome_watcher_command_line_win.h
diff --git a/chrome/app/chrome_watcher_command_line_win.h b/chrome/app/chrome_watcher_command_line_win.h
index 30ff98807a0a57ea6ab30f2d69a200609e3b99ad..800a4f0d2053b344448bb27a8d28a061bda31526 100644
--- a/chrome/app/chrome_watcher_command_line_win.h
+++ b/chrome/app/chrome_watcher_command_line_win.h
@@ -15,15 +15,21 @@ class FilePath;
 }  // namespace base
 
 // Generates a CommandLine that will launch |chrome_exe| in Chrome Watcher mode
-// to observe |parent_process|.
+// to observe |parent_process|. The watcher process will signal
+// |on_initialized_event| when its initialization is completed.

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

nit: "is complete" or "has completed"

[erikwright (departed), 2015/02/03 21:56:47]

Done.

 base::CommandLine GenerateChromeWatcherCommandLine(
     const base::FilePath& chrome_exe,
+    HANDLE on_initialized_event,

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

based on the comment above, i'd swap on_initialized_event and parent_process.
makes more sense to me that way for some reason.

[erikwright (departed), 2015/02/03 21:26:02]

We end up binding this to |chrome_exe|, and later to |on_initialized_event|, to
generate a Callback that only takes a single HANDLE.

If I reorder the parameters I'll need at least one "jump function" to swap the
order.

Let me know if you think it's warranted.

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

It took me a really long time to understand what you meant. Is it possible to
make it clear in the comments in either
ChromeWatcherClient::CommandLineGenerator or here that this is meant to be a
WatcherClient::CommandLineGenerator with an extra arg? I can't think of anything
graceful at the moment. My apologies for asking you to do something vague
without a concrete suggestion. :-(

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

I reversed the order to make the public contract intuitive at the expense of a
minor detour in the implementation. I think that's the right choice.

     HANDLE parent_process);
 
 // Interprets the Command Line used to launch a Chrome Watcher process and
-// extracts the parent process HANDLE. Verifies that the handle is usable in
-// this process before returning it, and returns NULL in case of a failure.
-base::win::ScopedHandle InterpretChromeWatcherCommandLine(
-    const base::CommandLine& command_line);
+// extracts the parent process and initialization event HANDLEs. Verifies that
+// the handles are usable in this process before returning them. Returns true if
+// both handles are successfully parsed and false otherwise. If only one of the
+// handles can be parsed, it will be closed.
+bool InterpretChromeWatcherCommandLine(
+    const base::CommandLine& command_line,
+    base::win::ScopedHandle* on_initialized_event,

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

i'd swap them here, too

[erikwright (departed), 2015/02/03 21:26:02]

Ordered for consistency with the above.

If you confirm the request to swap there I'll do it here too.

+    base::win::ScopedHandle* parent_process);
 
 #endif  // CHROME_APP_CHROME_WATCHER_COMMAND_LINE_WIN_H_