Gracefully exit when WebContents handler cannot create browser.

|ChromeWebContentsHandler::AddNewContents| assumed that a browser object
can be created in all situations but this is not true, at least if the
request comes during browser shutdown.

|ChromeWebContentsHandler::AddNewContents| is updated to consider the
case that browser cannot be created and gracefully exit.

Bug: 1141608, 1121894
Change-Id: Iaf0b2b4c1359ccf9b3b07ed606521a62c98ea4e3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2513209
Commit-Queue: Ramin Halavati <rhalavati@chromium.org>
Reviewed-by: Denis Kuznetsov [CET] <antrim@chromium.org>
Cr-Commit-Position: refs/heads/master@{#823517}

chrome/browser/ui/webui/chrome_web_contents_handler.cc

@@ -89,6 +89,14 @@ void ChromeWebContentsHandler::AddNewContents(
   Browser* browser = chrome::FindTabbedBrowser(profile, false);
   const bool browser_created = !browser;
   if (!browser) {
+    // TODO(https://crbug.com/1141608): Remove when root cause is found.
+    if (Browser::GetBrowserCreationStatusForProfile(profile) !=
+        Browser::BrowserCreationStatus::kOk) {
+      NOTREACHED() << "Browser creation status: "
+                   << static_cast<int>(
+                          Browser::GetBrowserCreationStatusForProfile(profile));
+      return;
+    }
     browser = Browser::Create(
         Browser::CreateParams(Browser::TYPE_NORMAL, profile, user_gesture));
   }