[proxies] Make Array.isArray respect proxies.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index 8f8908dc98a5346bb2f28c78072ae94222846c33..df0fe96089e4e7d58b7eb5ae1e2b58d41a2e3907 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -1052,6 +1052,9 @@ class Object {
   STRUCT_LIST(DECLARE_STRUCT_PREDICATE)
 #undef DECLARE_STRUCT_PREDICATE
 
+  // ES6, section 7.2.2 IsArray.  NOT to be confused with %_IsArray.
+  MUST_USE_RESULT static Maybe<bool> IsArray(Handle<Object> object);
+
   // ES6, section 7.2.3 IsCallable.
   INLINE(bool IsCallable() const);
 
@@ -9488,7 +9491,7 @@ class JSProxy: public JSReceiver {
 
   DECLARE_CAST(JSProxy)
 
-  bool IsRevoked();
+  bool IsRevoked() const;
 
   // ES6 9.5.1
   static MaybeHandle<Object> GetPrototype(Handle<JSProxy> receiver);