Extract locking behaviour from ProcessSingleton.

chrome/browser/chrome_browser_main.h

Index: chrome/browser/chrome_browser_main.h
diff --git a/chrome/browser/chrome_browser_main.h b/chrome/browser/chrome_browser_main.h
index cb663621eddcc1801b7deb24695adf4adae089bf..658b0bdafd18d6a7b3d881d70d0661b3951e2acc 100644
--- a/chrome/browser/chrome_browser_main.h
+++ b/chrome/browser/chrome_browser_main.h
@@ -12,6 +12,8 @@
 #include "chrome/browser/chrome_browser_field_trials.h"
 #include "chrome/browser/first_run/first_run.h"
 #include "chrome/browser/process_singleton.h"
+#include "chrome/browser/process_singleton_modal_dialog_lock.h"
+#include "chrome/browser/process_singleton_startup_lock.h"
 #include "chrome/browser/task_profiler/auto_tracking.h"
 #include "chrome/browser/ui/startup/startup_browser_creator.h"
 #include "content/public/browser/browser_main_parts.h"
@@ -167,6 +169,8 @@ class ChromeBrowserMainParts : public content::BrowserMainParts {
 
   // Android doesn't support multiple browser processes, so it doesn't implement
   // ProcessSingleton.
+  ProcessSingletonStartupLock startup_lock_;
+  ProcessSingletonModalDialogLock modal_dialog_lock_;
   scoped_ptr<ProcessSingleton> process_singleton_;

[Nico, 2013/04/17 21:04:24]

I started reviewing this a few times, and always got confused somewhere down the
road. I think my main problem is that I don't understand what all these locks
mean.

Can you add comments here that explain:
a) What each lock is for and when it's held
b) The locking hierarchy, i.e. the order these locks have to be obtained in
?

 #endif
   scoped_ptr<first_run::MasterPrefs> master_prefs_;