[proxies] Make Object.{freeze,seal} behave correctly for proxies.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index e39eb68b001438ab2de6a3cf2c544ba2cd6688bc..033f660956c87ee9254cf5f1f3b1799e5f83d412 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -1864,8 +1864,14 @@ class JSReceiver: public HeapObject {
   static bool GetOwnPropertyDescriptor(LookupIterator* it,
                                        PropertyDescriptor* desc);
 
-  // Disallow further properties to be added to the object.  This is
-  // ES6's [[PreventExtensions]] when passed DONT_THROW.
+  typedef PropertyAttributes IntegrityLevel;
+
+  // ES6 7.3.14 (when passed DONT_THROW)
+  // 'level' must be SEALED or FROZEN.
+  MUST_USE_RESULT static Maybe<bool> SetIntegrityLevel(
+      Handle<JSReceiver> object, IntegrityLevel lvl, ShouldThrow should_throw);
+
+  // ES6 [[PreventExtensions]] (when passed DONT_THROW)
   MUST_USE_RESULT static Maybe<bool> PreventExtensions(
       Handle<JSReceiver> object, ShouldThrow should_throw);
 
@@ -1919,6 +1925,13 @@ class JSReceiver: public HeapObject {
 
   enum KeyCollectionType { OWN_ONLY, INCLUDE_PROTOS };
 
+  // ES6 [[OwnPropertyKeys]] (modulo return type)
+  MUST_USE_RESULT static MaybeHandle<FixedArray> OwnPropertyKeys(
+      Handle<JSReceiver> object) {
+    return GetKeys(object, JSReceiver::OWN_ONLY, ALL_PROPERTIES,
+                   CONVERT_TO_STRING);
+  }
+
   // Computes the enumerable keys for a JSObject. Used for implementing
   // "for (n in object) { }".
   MUST_USE_RESULT static MaybeHandle<FixedArray> GetKeys(
@@ -2357,12 +2370,6 @@ class JSObject: public JSReceiver {
 
   static bool IsExtensible(Handle<JSObject> object);
 
-  // ES5 Object.seal
-  MUST_USE_RESULT static MaybeHandle<Object> Seal(Handle<JSObject> object);
-
-  // ES5 Object.freeze
-  MUST_USE_RESULT static MaybeHandle<Object> Freeze(Handle<JSObject> object);
-
   // Called the first time an object is observed with ES7 Object.observe.
   static void SetObserved(Handle<JSObject> object);