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

test/mjsunit/harmony/debug-stepin-proxies.js

Index: test/mjsunit/harmony/debug-stepin-proxies.js
diff --git a/test/mjsunit/harmony/debug-stepin-proxies.js b/test/mjsunit/harmony/debug-stepin-proxies.js
index 3775799de8f954cea185d35781e77f5713aab5e7..9c956ac45cb39f82876768071f3b06c55501c182 100644
--- a/test/mjsunit/harmony/debug-stepin-proxies.js
+++ b/test/mjsunit/harmony/debug-stepin-proxies.js
@@ -69,6 +69,10 @@ assertEquals([
   "d0", "l4d11", "m2d11",                           // [[Set]]
   "e14", "r4e14", "q4r11e14", "s2e14",              // for-in [[Enumerate]]
       "o6e14", "q4e14", "p6e14", "q4e14", "q4e14",  // exhaust iterator
-  "e9","f2","foo","e9","f2", "bar","e9",            // for-in body
+  "e9",                                             // for-in-body
+      "h4e9","i2e9",                                // [[Has]] property
+  "f2","foo", "e9",                                 // for-in-body
+    "h4e9","i2e9",                                  // [[Has]]property
+  "f2","bar", "e9",                                 // for-in-body
   "g0"
 ], log);