Clear old ARC instance before opt-in.

chrome/browser/chromeos/arc/arc_auth_service.cc

 // Copyright 2015 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/arc/arc_auth_service.h"
 
 #include <utility>
 
 #include "ash/shelf/shelf_delegate.h"
 #include "ash/shell.h"
@@ skipping 645 matching lines @@
 
 void ArcAuthService::DisableArc() {
   DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
   DCHECK(profile_);
   profile_->GetPrefs()->SetBoolean(prefs::kArcEnabled, false);
 }
 
 void ArcAuthService::StartUI() {
   DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
 
+  if (!arc_bridge_service()->stopped()) {
+    // If the user attempts to re-enable ARC while the bridge is still running
+    // the user should not be able to continue until the bridge has stopped.
+    ShowUI(UIPage::ERROR, l10n_util::GetStringUTF16(
+                              IDS_ARC_SIGN_IN_SERVICE_UNAVAILABLE_ERROR));
+    return;
+  }
+
   SetState(State::FETCHING_CODE);
 
   if (initial_opt_in_) {
     initial_opt_in_ = false;
     ShowUI(UIPage::TERMS_PROGRESS, base::string16());
   } else {
     context_->PrepareContext();
   }
 }
 
@@ skipping 75 matching lines @@
       return os << kStateFetchingCode;
     case ArcAuthService::State::ACTIVE:
       return os << kStateActive;
     default:
       NOTREACHED();
       return os;
   }
 }
 
 }  // namespace arc