repl: partially fix repl context

lib/repl.js

@@ -875,8 +875,11 @@ REPLServer.prototype.createContext = function() {
       context = vm.createContext();
     });
     for (const name of Object.getOwnPropertyNames(global)) {
-      Object.defineProperty(context, name,
-                            Object.getOwnPropertyDescriptor(global, name));
+      // Only set properties on the context that do not exist as primordial.
+      if (!(name in primordials)) {
+        Object.defineProperty(context, name,
+                              Object.getOwnPropertyDescriptor(global, name));
+      }
     }
     context.global = context;
     const _console = new Console(this.outputStream);

test/parallel/test-repl-context.js

@@ -16,11 +16,21 @@ const stream = new ArrayStream();
     useGlobal: false
   });
 
+  let output = '';
+  stream.write = function(d) {
+    output += d;
+  };
+
   // Ensure that the repl context gets its own "console" instance.
   assert(r.context.console);
 
   // Ensure that the repl console instance is not the global one.
   assert.notStrictEqual(r.context.console, console);
+  assert.notStrictEqual(r.context.Object, Object);
+
+  stream.run(['({} instanceof Object)']);
+
+  assert.strictEqual(output, 'true\n> ');
 
   const context = r.createContext();
   // Ensure that the repl context gets its own "console" instance.