cros: Rework LoginDisplayHostMojo::UpdateGaiaDialogVisibility

- drop LoginDisplayHost::default_host(), we're already in the default_host()
  instance
- remove early-return
- check if we're currently signing in, in which case do not show gaia (fixes the
  bug)

Bug: 852745
Change-Id: I5e1e7dcfca2c7aca55b9301721ea3499c1a88451
Reviewed-on: https://chromium-review.googlesource.com/1110273Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Jacob Dufault <jdufault@chromium.org>
Cr-Commit-Position: refs/heads/master@{#569771}

chrome/browser/chromeos/login/ui/login_display_host_mojo.cc

@@ -227,29 +227,35 @@ void LoginDisplayHostMojo::UpdateGaiaDialogVisibility(
     const base::Optional<AccountId>& prefilled_account) {
   DCHECK(dialog_);
 
+  bool is_signing_in = login_display_->IsSigninInProgress();
+
   if (visible) {
+    // Show the dialog.
+
     if (prefilled_account) {
       // Make sure gaia displays |account| if requested.
-      GetOobeUI()->GetGaiaScreenView()->ShowGaiaAsync(prefilled_account);
-      LoginDisplayHost::default_host()->LoadWallpaper(*prefilled_account);
+      if (!is_signing_in)
+        GetOobeUI()->GetGaiaScreenView()->ShowGaiaAsync(prefilled_account);
+
+      LoadWallpaper(*prefilled_account);
     } else {
-      LoginDisplayHost::default_host()->LoadSigninWallpaper();
+      LoadSigninWallpaper();
     }
 
     dialog_->Show(can_close /*closable_by_esc*/);
-    return;
-  }
-  // Show the wallpaper of the focused user pod when the dialog is hidden.
-  LoginDisplayHost::default_host()->LoadWallpaper(focused_pod_account_id_);
+  } else {
+    // Hide the dialog.
 
-  if (users_.empty() && GetOobeUI()) {
     // The dialog can not be closed if there is no user on the login screen.
     // Refresh the dialog instead.
-    GetOobeUI()->GetGaiaScreenView()->ShowGaiaAsync(base::nullopt);
-    return;
-  }
+    if (!is_signing_in && users_.empty() && GetOobeUI()) {
+      GetOobeUI()->GetGaiaScreenView()->ShowGaiaAsync(base::nullopt);
+      return;
+    }
 
-  dialog_->Hide();
+    LoadWallpaper(focused_pod_account_id_);
+    dialog_->Hide();
+  }
 }
 
 void LoginDisplayHostMojo::UpdateGaiaDialogSize(int width, int height) {

chrome/browser/chromeos/login/ui/login_display_mojo.cc

@@ -6,7 +6,6 @@
 
 #include "chrome/browser/chrome_notification_types.h"
 #include "chrome/browser/chromeos/accessibility/accessibility_manager.h"
-#include "chrome/browser/chromeos/login/existing_user_controller.h"
 #include "chrome/browser/chromeos/login/screens/chrome_user_selection_screen.h"
 #include "chrome/browser/chromeos/login/screens/user_selection_screen.h"
 #include "chrome/browser/chromeos/login/ui/login_display_host_mojo.h"
@@ -152,12 +151,13 @@ void LoginDisplayMojo::ShowUnrecoverableCrypthomeErrorDialog() {
 
 void LoginDisplayMojo::Login(const UserContext& user_context,
                              const SigninSpecifics& specifics) {
-  if (host_)
-    host_->existing_user_controller()->Login(user_context, specifics);
+  if (delegate_)
+    delegate_->Login(user_context, specifics);
 }
 
 bool LoginDisplayMojo::IsSigninInProgress() const {
-  NOTIMPLEMENTED();
+  if (delegate_)
+    return delegate_->IsSigninInProgress();
   return false;
 }
 
@@ -232,8 +232,7 @@ bool LoginDisplayMojo::AllowNewUserChanged() const {
 }
 
 bool LoginDisplayMojo::IsUserSigninCompleted() const {
-  NOTIMPLEMENTED();
-  return false;
+  return is_signin_completed();
 }
 
 void LoginDisplayMojo::HandleGetUsers() {