Fix sketchy User Manager code :(

chrome/browser/ui/webui/signin/user_manager_screen_handler.cc

Index: chrome/browser/ui/webui/signin/user_manager_screen_handler.cc
diff --git a/chrome/browser/ui/webui/signin/user_manager_screen_handler.cc b/chrome/browser/ui/webui/signin/user_manager_screen_handler.cc
index 2bea73cf61f7e925c5adcda4b3dda15a66e52a20..5d8a67eda08bc9e0673ec0dff01f3491e49dec9e 100644
--- a/chrome/browser/ui/webui/signin/user_manager_screen_handler.cc
+++ b/chrome/browser/ui/webui/signin/user_manager_screen_handler.cc
@@ -80,6 +80,16 @@ void OpenNewWindowForProfile(
     false);
 }
 
+// This callback is run after switching to a new profile has finished. This
+// means either a new browser window has been opened, or an existing one
+// has been found, which means we can safely close the User Manager without
+// accidentally terminating the browser process.
+void OnSwitchToProfileComplete() {
+  base::MessageLoop::current()->PostTask(

[Alexei Svitkine (slow), 2014/02/06 22:02:12]

Your comment should explain why this is posted rather than executed directly.

[noms (inactive), 2014/02/06 22:51:34]

Done.

+        FROM_HERE,
+        base::Bind(&chrome::HideUserManager));
+}
+
 std::string GetAvatarImageAtIndex(
     size_t index, const ProfileInfoCache& info_cache) {
   bool is_gaia_picture =
@@ -185,7 +195,7 @@ void UserManagerScreenHandler::HandleInitialize(const base::ListValue* args) {
 
 void UserManagerScreenHandler::HandleAddUser(const base::ListValue* args) {
   profiles::CreateAndSwitchToNewProfile(desktop_type_,
-                                        base::Bind(&chrome::HideUserManager),
+                                        base::Bind(&OnSwitchToProfileComplete),
                                         ProfileMetrics::ADD_NEW_USER_MANAGER);
 }
 
@@ -263,7 +273,7 @@ void UserManagerScreenHandler::HandleRemoveUser(const base::ListValue* args) {
 
 void UserManagerScreenHandler::HandleLaunchGuest(const base::ListValue* args) {
   profiles::SwitchToGuestProfile(desktop_type_,
-                                 base::Bind(&chrome::HideUserManager));
+                                 base::Bind(&OnSwitchToProfileComplete));
   ProfileMetrics::LogProfileSwitchUser(ProfileMetrics::SWITCH_PROFILE_GUEST);
 }
 
@@ -300,7 +310,7 @@ void UserManagerScreenHandler::HandleLaunchUser(const base::ListValue* args) {
   profiles::SwitchToProfile(path,
                             desktop_type_,
                             false,  /* reuse any existing windows */
-                            base::Bind(&chrome::HideUserManager),
+                            base::Bind(&OnSwitchToProfileComplete),
                             ProfileMetrics::SWITCH_PROFILE_MANAGER);
 }
 
@@ -472,7 +482,7 @@ void UserManagerScreenHandler::ReportAuthenticationResult(
     base::FilePath path = info_cache.GetPathOfProfileAtIndex(
         authenticating_profile_index_);
     profiles::SwitchToProfile(path, desktop_type_, true,
-                              base::Bind(&chrome::HideUserManager),
+                              base::Bind(&OnSwitchToProfileComplete),
                               ProfileMetrics::SWITCH_PROFILE_UNLOCK);
   } else {
     web_ui()->CallJavascriptFunction(