Check for browser shutdown before launching crOS AccountManager

This is related to https://crrev.com/c/1903365 - with the additional
check that |g_browser_process| may be abnormally shutting down without
|chrome::IsAttemptingShutdown| being true - which happens only for a
clean, user attempted shutdown.

Bug: 1121894
Change-Id: I6d4aa7de8998ad0c621f0fc17a17853924cfd342
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2385437Reviewed-by: Roman Sorokin [CET] <rsorokin@chromium.org>
Commit-Queue: Kush Sinha <sinhak@chromium.org>
Cr-Commit-Position: refs/heads/master@{#803108}

chrome/browser/ui/webui/chromeos/account_manager/account_manager_welcome_dialog.cc

@@ -7,6 +7,7 @@
 #include <string>
 
 #include "base/check_op.h"
+#include "chrome/browser/browser_process.h"
 #include "chrome/browser/lifetime/application_lifetime.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/profiles/profile_manager.h"
@@ -83,8 +84,9 @@ void AccountManagerWelcomeDialog::AdjustWidgetInitParams(
 
 void AccountManagerWelcomeDialog::OnDialogClosed(
     const std::string& json_retval) {
-  // Opening Settings during shutdown leads to a crash.
-  if (!chrome::IsAttemptingShutdown()) {
+  // Opening Settings during shutdown or crash/restart leads to a crash.
+  if (!chrome::IsAttemptingShutdown() && g_browser_process &&
+      !g_browser_process->IsShuttingDown()) {
     chrome::SettingsWindowManager::GetInstance()->ShowOSSettings(
         ProfileManager::GetActiveUserProfile(),
         chromeos::settings::mojom::kMyAccountsSubpagePath);