Add debug code to help understand SEGV in ~ErrorScreen.

BUG=396557

Review URL: https://codereview.chromium.org/424613003

Cr-Commit-Position: refs/heads/master@{#289279}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@289279 0039d316-1c4b-4281-b951-d872f2087c98

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

@@ -11,20 +11,29 @@
 #include "chrome/browser/chromeos/login/wizard_controller.h"
 #include "chrome/browser/chromeos/settings/cros_settings.h"
 
+namespace {
+void* const kCanaryConstant = (void*)0xbaddecafbaddecafLLU;
+}
+
 namespace chromeos {
 
 ErrorScreen::ErrorScreen(ScreenObserver* screen_observer,
                          ErrorScreenActor* actor)
     : WizardScreen(screen_observer),
+      canary_1_(kCanaryConstant),
       actor_(actor),
+      canary_2_(kCanaryConstant),
       parent_screen_(OobeDisplay::SCREEN_UNKNOWN),
       weak_factory_(this) {
-  DCHECK(actor_);
+  CHECK(actor_);
   actor_->SetDelegate(this);
 }
 
 ErrorScreen::~ErrorScreen() {
-  if (actor_)
+  CHECK(this);
+  CHECK(canary_1_ == kCanaryConstant);
+  CHECK(canary_2_ == kCanaryConstant);
+  CHECK(actor_);
   actor_->SetDelegate(NULL);
 }
 

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

@@ -103,7 +103,9 @@ class ErrorScreen : public WizardScreen,
   void StartGuestSessionAfterOwnershipCheck(
       DeviceSettingsService::OwnershipStatus ownership_status);
 
+  void* volatile canary_1_;  // For debugging of https://crbug.com/396557.
   ErrorScreenActor* actor_;
+  void* volatile canary_2_;
 
   OobeDisplay::Screen parent_screen_;