[proxies] Implement [[Delete]].

src/runtime/runtime-scopes.cc

Index: src/runtime/runtime-scopes.cc
diff --git a/src/runtime/runtime-scopes.cc b/src/runtime/runtime-scopes.cc
index 49320b2a42be7f140c5e6647a6e6fbf1764a2e5b..3cca35b14aef2153a95740fb62ba029c9c013789 100644
--- a/src/runtime/runtime-scopes.cc
+++ b/src/runtime/runtime-scopes.cc
@@ -903,10 +903,9 @@ RUNTIME_FUNCTION(Runtime_DeleteLookupSlot) {
   // the global object, or the subject of a with.  Try to delete it
   // (respecting DONT_DELETE).
   Handle<JSObject> object = Handle<JSObject>::cast(holder);
-  Handle<Object> result;
-  ASSIGN_RETURN_FAILURE_ON_EXCEPTION(isolate, result,
-                                     JSReceiver::DeleteProperty(object, name));
-  return *result;
+  Maybe<bool> result = JSReceiver::DeleteProperty(object, name);
+  MAYBE_RETURN(result, isolate->heap()->exception());
+  return isolate->heap()->ToBoolean(result.FromJust());
 }