[proxy] fixing harmony/proxy.js tests and improving error messages + some drive-by fixes

src/js/v8natives.js

 // Copyright 2012 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.
 
 (function(global, utils) {
 
 %CheckIsBootstrapping();
 
 // ----------------------------------------------------------------------------
 // Imports
@@ skipping 551 matching lines @@
 
 // Harmony proxies.
 function DefineProxyProperty(obj, p, attributes, should_throw) {
   // TODO(rossberg): adjust once there is a story for symbols vs proxies.
   if (IS_SYMBOL(p)) return false;
 
   var handler = %GetHandler(obj);
   var result = CallTrap2(handler, "defineProperty", UNDEFINED, p, attributes);
   if (!result) {
     if (should_throw) {
-      throw MakeTypeError(kProxyHandlerReturned,
+      throw MakeTypeError(kProxyTrapReturned,
                           handler, "false", "defineProperty");
     } else {
       return false;
     }
   }
   return true;
 }
 
 
 // ES6 9.1.6 [[DefineOwnProperty]](P, Desc)
@@ skipping 935 matching lines @@
   to.ObjectToString = ObjectToString;
 });
 
 %InstallToContext([
   "global_eval_fun", GlobalEval,
   "object_value_of", ObjectValueOf,
   "object_to_string", ObjectToString,
 ]);
 
 })