Issue 5552 - use strict mode for all JS in libadblocklus

src/JsEngine.cpp

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-2017 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 30 matching lines @@
 
   void CheckTryCatch(const v8::TryCatch& tryCatch)
   {
     if (tryCatch.HasCaught())
       throw AdblockPlus::JsError(tryCatch.Exception(), tryCatch.Message());
   }
 
   class V8Initializer
   {
     V8Initializer()
-      : platform(v8::platform::CreateDefaultPlatform())
+      : platform{nullptr}
     {
+      std::string cmd = "--use_strict";
+      v8::V8::SetFlagsFromString(cmd.c_str(), cmd.length());
+      platform = v8::platform::CreateDefaultPlatform();
       v8::V8::InitializePlatform(platform);
       v8::V8::Initialize();
     }
 
     ~V8Initializer()
     {
       v8::V8::Dispose();
       v8::V8::ShutdownPlatform();
       delete platform;
     }
@@ skipping 234 matching lines @@
     list.push_back(JsValue(shared_from_this(), arguments[i]));
   return list;
 }
 
 void AdblockPlus::JsEngine::SetGlobalProperty(const std::string& name,
                                               const AdblockPlus::JsValue& value)
 {
   auto global = GetGlobalObject();
   global.SetProperty(name, value);
 }