[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..bfd63e49e054a3c6b6638a59fda10f564eb2820f 100644
--- a/test/mjsunit/harmony/regress/regress-crbug-461520.js
+++ b/test/mjsunit/harmony/regress/regress-crbug-461520.js
@@ -7,7 +7,7 @@
 var fuse = 1;
 var handler = {
   get: function() { return function() {} },
-  getPropertyDescriptor: function() {
+  getOwnPropertyDescriptor: function() {
     if (fuse-- == 0) throw "please die";
     return {value: function() {}, configurable: true};
   }