[runtime] [proxy] implementing [[Get]] trap.

test/mjsunit/harmony/proxies-get-prototype-of.js

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Flags: --harmony-proxies
 
 var target = { target: 1 };
 target.__proto__ = {};
 var handler = { handler: 1 };
 var proxy = new Proxy(target, handler);
 
 assertSame(Object.getPrototypeOf(proxy), target.__proto__ );
 
 target.__proto__ = [];
 assertSame(Object.getPrototypeOf(proxy), target.__proto__);
 
 handler.getPrototypeOf = function() {
   return 1;
 }
 assertThrows(function() { Object.getPrototypeOf(proxy) }, TypeError);
 
 var target_prototype = {a:1, b:2};
 handler.getPrototypeOf = function() {
   return target_prototype ;
 }
 assertSame(Object.getPrototypeOf(proxy), target_prototype);
 
 // Test with proxy target:
-var proxy2 = new Proxy(proxy, {});
+var proxy2 = new Proxy(proxy, {'handler':1});
 assertSame(Object.getPrototypeOf(proxy2), target_prototype);
 
 // Test with Proxy handler:
-// TODO(neis,cbruni): Uncomment once the get trap works again.
-// var proxy3_prototype = {};
-// var handler_proxy = new Proxy({
-//   getPrototypeOf: function() { return proxy3_prototype }
-// }, {});
-// var proxy3 = new Proxy(target, handler_proxy);
-// assertSame(Object.getPrototypeOf(proxy3), target_prototype);
+var proxy3_prototype = {'proto3':true};
+var handler_proxy = new Proxy({
+  getPrototypeOf: function() { return proxy3_prototype }
+}, {});
+var proxy3 = new Proxy(target, handler_proxy);
+assertSame(Object.getPrototypeOf(proxy3), proxy3_prototype);