ES6 symbols: symbol properties should not cause going into slow mode.

R=yangguo@chromium.org
BUG=

Review URL: https://codereview.chromium.org/13042013

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@14089 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/objects.cc

@@ -1733,7 +1733,7 @@ MaybeObject* JSObject::AddFastProperty(Name* name,
   // hidden strings) and is not a real identifier.
   // Normalize the object if it will have too many fast properties.
   Isolate* isolate = GetHeap()->isolate();
-  if ((!IsIdentifier(isolate->unicode_cache(), name)
+  if ((!name->IsSymbol() && !IsIdentifier(isolate->unicode_cache(), name)
        && name != isolate->heap()->hidden_string()) ||
       (map()->unused_property_fields() == 0 &&
        TooManyFastProperties(properties()->length(), store_mode))) {

test/mjsunit/harmony/symbols.js

@@ -213,9 +213,12 @@ TestCollections()
 
 
 function TestKeySet(obj) {
+  assertTrue(%HasFastProperties(obj))
   // Set the even symbols via assignment.
   for (var i = 0; i < symbols.length; i += 2) {
     obj[symbols[i]] = i
+    // Object should remain in fast mode until too many properties were added.
+    assertTrue(%HasFastProperties(obj) || i >= 30)
   }
 }