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

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

Index: chrome/browser/ui/views/profiles/user_manager_view.cc
diff --git a/chrome/browser/ui/views/profiles/user_manager_view.cc b/chrome/browser/ui/views/profiles/user_manager_view.cc
index e3cc5d31421c4bb4a10c7d022710bd95fb1e4abe..812f09af6d049caa0c3d1e293bfd87a0db92b6fb 100644
--- a/chrome/browser/ui/views/profiles/user_manager_view.cc
+++ b/chrome/browser/ui/views/profiles/user_manager_view.cc
@@ -287,6 +287,10 @@ 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,