Oilpan: reliably track listening PlatformEventControllers.

Source/core/frame/PlatformEventDispatcher.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 "core/frame/PlatformEventDispatcher.h"
 
 #include "core/frame/PlatformEventController.h"
 #include "wtf/TemporaryChange.h"
 
@@ skipping 23 matching lines @@
     // Do not actually remove the controller from the vector, instead zero them out.
     // The zeros are removed in these two cases:
     // 1. either immediately if we are not dispatching any events,
     // 2. or after events to all controllers have dispatched (see notifyControllers()).
     // This is to correctly handle the re-entrancy case when a controller is destroyed
     // while the events are still being dispatched.
     size_t index = m_controllers.find(controller);
     if (index == kNotFound)
         return;
 
-    m_controllers[index] = 0;
+    m_controllers[index] = nullptr;
     m_needsPurge = true;
 
     if (!m_isDispatching)
         purgeControllers();
 }
 
 void PlatformEventDispatcher::purgeControllers()
 {
     ASSERT(m_needsPurge);
 
@@ skipping 23 matching lines @@
             if (m_controllers[i])
                 m_controllers[i]->didUpdateData();
         }
     }
 
     if (m_needsPurge)
         purgeControllers();
 }
 
 } // namespace blink