Implement set trap for proxies, and revamp class hierarchy in preparation

src/runtime.cc

Index: src/runtime.cc
diff --git a/src/runtime.cc b/src/runtime.cc
index 1b8abf0dc932cc44d09dfda4b80a855187b0e02f..4997d56df54b8dceb95b98938b0bff0dca4283d7 100644
--- a/src/runtime.cc
+++ b/src/runtime.cc
@@ -3721,8 +3721,7 @@ MaybeObject* Runtime::GetObjectProperty(Isolate* isolate,
   if (name->AsArrayIndex(&index)) {
     return GetElementOrCharAt(isolate, object, index);
   } else {
-    PropertyAttributes attr;
-    return object->GetProperty(*name, &attr);
+    return object->GetProperty(*name);
   }
 }