BatteryManager.getBattery(): gracefully bail on context-detached use.

Source/modules/battery/BatteryManager.cpp

 // 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 "config.h"
 #include "modules/battery/BatteryManager.h"
 
 #include "core/dom/Document.h"
 #include "core/events/Event.h"
 #include "modules/battery/BatteryDispatcher.h"
@@ skipping 25 matching lines @@
 }
 
 ScriptPromise BatteryManager::startRequest(ScriptState* scriptState)
 {
     if (m_state == Pending)
         return m_resolver->promise();
 
     m_resolver = ScriptPromiseResolver::create(scriptState);
     ScriptPromise promise = m_resolver->promise();
 
-    ASSERT(executionContext());
     // If the context is in a stopped state already, do not start updating.
-    if (m_state == Resolved || executionContext()->activeDOMObjectsAreStopped()) {
+    if (m_state == Resolved || !executionContext() || executionContext()->activeDOMObjectsAreStopped()) {
         // FIXME: Consider returning the same promise in this case. See crbug.com/385025.
         m_state = Resolved;
         m_resolver->resolve(this);
     } else if (m_state == NotStarted) {
         m_state = Pending;
         m_hasEventListener = true;
         startUpdating();
     }
 
     return promise;
@@ skipping 95 matching lines @@
 DEFINE_TRACE(BatteryManager)
 {
     visitor->trace(m_resolver);
     visitor->trace(m_batteryStatus);
     PlatformEventController::trace(visitor);
     RefCountedGarbageCollectedEventTargetWithInlineData<BatteryManager>::trace(visitor);
     ActiveDOMObject::trace(visitor);
 }
 
 } // namespace blink