Proxy passed as vm context hides built-in properties. #6158

• Version: v6.0.0-pre (node-vee-eight-4.9, node-vee-eight-5.0)
• Platform: Linux ubuntu 4.2.0-35-generic Working with nvm, nvmw and similar installation managers #40-Ubuntu SMP Tue Mar 15 22:15:45 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux

Proxy object is not correctly contextified by vm.createContext routine.

I've tried to create vm with traps on global context, so I made one based on Proxy object.
Unfortunately, code executed inside vm doesn't have any access to built-ins.

> vm.runInNewContext("String", {})
[Function: String]
> vm.runInNewContext("String", new Proxy({},{}))
undefined

Passing required built-ins this way:

ctx = new Proxy({String:String}, {})
vm.runInNewContext("String", ctx)

seems to be (a bit dirty) workaround, but it doesn't resolve a problem at all...

vm.runInNewContext("String.prototype.f = function(){}; ''.f()", ctx)
... because passed String differs from used built-in by string literal, so this code raises an exception (''.f is undefined)

Tested on builds from branches node-vee-eight-4.9/5.0
Proxies doesn't work with older V8s and VMs, because of "not an object" bug.