Issue #3594 - Remove `globalJsObject` and add `GetGlobalObject()`

src/JsEngine.cpp

 /*
  * 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 79 matching lines @@
   const v8::HandleScope handleScope(result->GetIsolate());
 
   result->context.reset(new v8::Persistent<v8::Context>(result->GetIsolate(),
     v8::Context::New(result->GetIsolate())));
   AdblockPlus::GlobalJsObject::Setup(result, appInfo, result->GetGlobalObject());
   return result;
 }
 
 AdblockPlus::JsValuePtr AdblockPlus::JsEngine::GetGlobalObject()
 {
-  const auto i = GetIsolate();

[sergei, 2016/11/28 15:04:33]

Why not to use JsContext context(shared_from_this());?

[Eric, 2016/11/28 15:33:24]

That should work. The code here is a minimal extraction refactoring from the
existing code, which meant that I just copied the existing statements over. I'll
see if this works. If it works here, it's probably also the right thing to do in
New() as well, where I copied it from.

One of the things I've wondered looking at this code the last couple of days is
why there's a separate context class at all. Evidently others are using
`v8::Persistent` to hold a single context, which would get rid of a bunch of
overhead creating it each time it's needed.

-  const v8::Locker locker(i);
-  const v8::Isolate::Scope isolateScope(i);
-  const v8::HandleScope handleScope(i);
-  return JsValuePtr(new JsValue(shared_from_this(), v8::Local<v8::Context>::New(i, *context)->Global()));
-};
+  JsContext context(shared_from_this());
+  return JsValuePtr(new JsValue(shared_from_this(), context.GetV8Context()->Global()));
+}
 
 AdblockPlus::JsValuePtr AdblockPlus::JsEngine::Evaluate(const std::string& source,
     const std::string& filename)
 {
   const JsContext context(shared_from_this());
   const v8::TryCatch tryCatch;
   const v8::Handle<v8::Script> script = CompileScript(GetIsolate(), source,
     filename);
   CheckTryCatch(tryCatch);
   v8::Local<v8::Value> result = script->Run();
@@ skipping 132 matching lines @@
 
 
 void AdblockPlus::JsEngine::SetGlobalProperty(const std::string& name, 
                                               AdblockPlus::JsValuePtr value)
 {
   auto global = GetGlobalObject();
   if (!global)
     throw std::runtime_error("Global object cannot be null");
   global->SetProperty(name, value);
 }