[proxies] Implement [[Enumerate]] and [[OwnPropertyKeys]]

src/key-accumulator.cc

Index: src/key-accumulator.cc
diff --git a/src/key-accumulator.cc b/src/key-accumulator.cc
index 91b014aacd7b688f521ebb7e131d4d0dcd76a2cb..68fe9d8cb70df5d0ab0ae2f7864d272266ec8d77 100644
--- a/src/key-accumulator.cc
+++ b/src/key-accumulator.cc
@@ -217,6 +217,18 @@ void KeyAccumulator::AddKeysFromProxy(Handle<JSObject> array_like) {
 }
 
 
+void KeyAccumulator::AddKeysFromProxy(Handle<FixedArray> keys) {
+  // Proxies define a complete list of keys with no distinction of
+  // elements and properties, which breaks the normal assumption for the
+  // KeyAccumulator.
+  AddKeys(keys, PROXY_MAGIC);
+  // Invert the current length to indicate a present proxy, so we can ignore
+  // element keys for this level. Otherwise we would not fully respect the order
+  // given by the proxy.
+  level_string_length_ = -level_string_length_;
+}
+
+
 void KeyAccumulator::AddElementKeysFromInterceptor(
     Handle<JSObject> array_like) {
   AddKeys(array_like, CONVERT_TO_ARRAY_INDEX);