* Electron version: 1.7.3
* Operating system: Windows, MacOS, Linux

### Expected behavior
Context Isolation should work when sandbox option is set to true

### Actual behavior
Context Isolation should work when sandbox option is set to true

### How to reproduce

Turn on contextIsolation and sandbox on browser window. contextIsolation doesn't work. 

contextIsolation work needs to happen on sandbox renderer client as well. 

cc: @tarruda @kevinsawicki @chandrachivukula
atom/renderer/atom_renderer_client.cc
v8::Isolate* isolate = context->GetIsolate();
  
  
  std::string bundle(node::isolated_bundle_data,
      node::isolated_bundle_data + sizeof(node::isolated_bundle_data));
  std::string wrapper = "(function (binding, require) {\n" + bundle + "\n})";
  auto script = v8::Script::Compile(
      mate::ConvertToV8(isolate, wrapper)->ToString());
  auto func = v8::Handle<v8::Function>::Cast(
      script->Run(context).ToLocalChecked());
  auto binding = v8::Object::New(isolate);
  api::Initialize(binding, v8::Null(isolate), context, nullptr);
  
  base::CommandLine* command_line = base::CommandLine::ForCurrentProcess();
  mate::Dictionary dict(isolate, binding);
  if (command_line->HasSwitch(switches::kGuestInstanceID))
    dict.Set(options::kGuestInstanceID,
             command_line->GetSwitchValueASCII(switches::kGuestInstanceID));
  if (command_line->HasSwitch(switches::kOpenerID))
    dict.Set(options::kOpenerID,
             command_line->GetSwitchValueASCII(switches::kOpenerID));
  dict.Set("hiddenPage", command_line->HasSwitch(switches::kHiddenPage));
  dict.Set("nativeWindowOpen",
           command_line->HasSwitch(switches::kNativeWindowOpen));
  v8::Local<v8::Value> args[] = { binding };
  ignore_result(func->Call(context, v8::Null(isolate), 1, args));
}
}