Issue #4694 - Add mutex protection to JS event handling

include/AdblockPlus/JsEngine.h

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-2016 Eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 22 matching lines @@
 namespace v8
 {
   class Arguments;
   class Isolate;
   class Value;
   class Context;
   template<class T> class Handle;
   typedef Handle<Value>(*InvocationCallback)(const Arguments &args);
 }
 
+/*
+ * Forward declaration of internally-defined implementation class
+ */
+class JsEngineInternal;
+
 namespace AdblockPlus
 {
   class JsEngine;
 
   /**
    * Shared smart pointer to a `JsEngine` instance.
    */
   typedef std::shared_ptr<JsEngine> JsEnginePtr;
 
   /**
@@ skipping 221 matching lines @@
     explicit JsEngine(const ScopedV8IsolatePtr& isolate);
 
     /**
      * Retrieve the global object as a JsValuePtr
      * 
      * \par Precondition
      * - Requires a v8 execution scope already present
      */
     JsValuePtr GetGlobalObject();
 
+    /**
+     * Provide a reference to this object in its type as constructed.
+     * Objects of this type are only ever constructed as `JsEngineInternal`.
+     */
+    JsEngineInternal& Internal();
+
     /// Isolate must be disposed only after disposing of all objects which are
     /// using it.
     ScopedV8IsolatePtr isolate;
 
     FileSystemPtr fileSystem;
     WebRequestPtr webRequest;
     LogSystemPtr logSystem;
-    EventMap eventCallbacks;
 
     // Forward declaration for PImpl idiom
     class SchedulerImpl;
     /**
      * Scheduler for tasks executed under the current engine.
      *
      * \par Invariant
      *   `bool(scheduler)` is always true
      */
     std::unique_ptr<SchedulerImpl> scheduler;
   };
 }
 
 #endif