Display signin dialog for the default profile after the last profile being deleted.

chrome/browser/ui/views/profiles/user_manager_view.cc

 // Copyright 2014 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/ui/views/profiles/user_manager_view.h"
 
 #include "base/callback.h"
 #include "base/memory/ptr_util.h"
 #include "base/time/time.h"
 #include "build/build_config.h"
@@ skipping 269 matching lines @@
 
   DCHECK(!instance_);
   instance_ = instance.release();  // |instance_| takes over ownership.
   instance_->Init(system_profile, GURL(url));
 }
 
 void UserManagerView::ShowReauthDialog(content::BrowserContext* browser_context,
                                        const std::string& email,
                                        signin_metrics::Reason reason) {
   HideReauthDialog();
+  // if there is no |browser_context| provided, using the one belongs to the
+  // UserManagerView.
+  if (browser_context == nullptr)

[sky, 2016/10/04 18:22:27]

This seems wrong to me. How is it that web_view_ would have the right
BrowserContext, but it wouldn't be passed to this function?

+    browser_context = web_view_->browser_context();
   // The dialog delegate will be deleted when the widget closes. The created
   // WebView's lifetime is managed by the delegate.
   delegate_ = new ReauthDelegate(this,
                                  new views::WebView(browser_context),
                                  email,
                                  reason);
   gfx::NativeView parent = instance_->GetWidget()->GetNativeView();
   views::DialogDelegate::CreateDialogWidget(delegate_, nullptr, parent);
   delegate_->GetWidget()->Show();
 }
@@ skipping 138 matching lines @@
     delegate_->DisplayErrorMessage();
 }
 
 void UserManagerView::SetSigninProfilePath(const base::FilePath& profile_path) {
   signin_profile_path_ = profile_path;
 }
 
 base::FilePath UserManagerView::GetSigninProfilePath() {
   return signin_profile_path_;
 }