Add debug code to help understand SEGV in ~ErrorScreen.

chrome/browser/chromeos/login/screens/error_screen.h

Index: chrome/browser/chromeos/login/screens/error_screen.h
diff --git a/chrome/browser/chromeos/login/screens/error_screen.h b/chrome/browser/chromeos/login/screens/error_screen.h
index 97657780c7118b1682d662c26fb3f1badc444df3..a854816afe81ebad799f69b859500f40a42155f0 100644
--- a/chrome/browser/chromeos/login/screens/error_screen.h
+++ b/chrome/browser/chromeos/login/screens/error_screen.h
@@ -103,7 +103,9 @@ class ErrorScreen : public WizardScreen,
   void StartGuestSessionAfterOwnershipCheck(
       DeviceSettingsService::OwnershipStatus ownership_status);
 
+  volatile void* canary_1_;  // For debugging of https://crbug.com/396557.

[ygorshenin1, 2014/08/13 08:36:51]

As you're just reading pointer's value, not a value pointers point to, you can
simply replace "void*" by "long" - it has the same size as a pointer but less
obfuscating.

[Thiemo Nagel, 2014/08/13 09:38:48]

The sizes of pointer and long depend on the data model.  Although I'm inclined
to believe that sizeof(void*)==sizeof(long) for all architectures supported by
Chromium OS, technically there is no guarantee for that and thus I think that
it's actually less obfuscating to use void* here.  (For example Windows 64bit
uses the LLP64 data model where sizeof(void*)==8 and sizeof(long)==4.)

What do you think?

   ErrorScreenActor* actor_;
+  volatile void* canary_2_;
 
   OobeDisplay::Screen parent_screen_;