Revert "Speculative revert by sheriff"

chrome/browser/chromeos/login/helper.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/chromeos/login/helper.h"
 
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/strings/utf_string_conversions.h"
 #include "chrome/browser/chromeos/login/startup_utils.h"
@@ skipping 135 matching lines @@
   content::WebContents* embedder = GetLoginWebContents();
   if (!embedder)
     return nullptr;
 
   // Note the partition name must match the sign-in webview used. For now,
   // this is the default unnamed, shared, in-memory partition.
   return GetPartition(embedder, std::string());
 }
 
 net::URLRequestContextGetter* GetSigninContext() {
-  if (StartupUtils::IsWebviewSigninEnabled())
-    return GetSigninPartition()->GetURLRequestContext();
+  if (StartupUtils::IsWebviewSigninEnabled()) {
+    content::StoragePartition* signin_partition = GetSigninPartition();
+
+    // Special case for unit tests. There's no LoginDisplayHost thus no
+    // webview instance. TODO(nkostylev): Investigate if there's a better
+    // place to address this like dependency injection. http://crbug.com/477402
+    if (!signin_partition && !LoginDisplayHostImpl::default_host())
+      return ProfileHelper::GetSigninProfile()->GetRequestContext();
+
+    if (!signin_partition)
+      return nullptr;
+
+    return signin_partition->GetURLRequestContext();
+  }
 
   return ProfileHelper::GetSigninProfile()->GetRequestContext();
 }
 
 }  // namespace login
 
 }  // namespace chromeos