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

test/mjsunit/harmony/regress/regress-crbug-461520.js

Index: test/mjsunit/harmony/regress/regress-crbug-461520.js
diff --git a/test/mjsunit/harmony/regress/regress-crbug-461520.js b/test/mjsunit/harmony/regress/regress-crbug-461520.js
index 5239ecb6cae602b4d27da01af1841c8de7d0f6ac..7ef9e2052055c16b549e9f936a5d6c02bb4b8a58 100644
--- a/test/mjsunit/harmony/regress/regress-crbug-461520.js
+++ b/test/mjsunit/harmony/regress/regress-crbug-461520.js
@@ -5,9 +5,11 @@
 // Flags: --harmony-proxies
 
 var fuse = 1;
+
 var handler = {
   get: function() { return function() {} },
-  getPropertyDescriptor: function() {
+  has() { return true },
+  getOwnPropertyDescriptor: function() {
     if (fuse-- == 0) throw "please die";
     return {value: function() {}, configurable: true};
   }