[es6] JSObject::GetOwnElementKeys should collect String wrapper keys first

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index aeb6bb5fe79dcc76682a389f2620fde06493121e..df5ffcfd20989cde9822f34e278f6051c1c087ee 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -12972,6 +12972,23 @@ int JSObject::NumberOfEnumElements() {
 int JSObject::GetOwnElementKeys(FixedArray* storage,
                                 PropertyAttributes filter) {
   int counter = 0;
+
+  // If this is a String wrapper, add the string indices first,
+  // as they're guaranteed to preced the elements in numerical order
+  // and ascending order is required by ECMA-262, 6th, 9.1.12.
+  if (IsJSValue()) {
+    Object* val = JSValue::cast(this)->value();
+    if (val->IsString()) {
+      String* str = String::cast(val);
+      if (storage) {
+        for (int i = 0; i < str->length(); i++) {
+          storage->set(counter + i, Smi::FromInt(i));
+        }
+      }
+      counter += str->length();
+    }
+  }
+
   switch (GetElementsKind()) {
     case FAST_SMI_ELEMENTS:
     case FAST_ELEMENTS:
@@ -13078,18 +13095,6 @@ int JSObject::GetOwnElementKeys(FixedArray* storage,
     }
   }
 
-  if (this->IsJSValue()) {
-    Object* val = JSValue::cast(this)->value();
-    if (val->IsString()) {
-      String* str = String::cast(val);
-      if (storage) {
-        for (int i = 0; i < str->length(); i++) {
-          storage->set(counter + i, Smi::FromInt(i));
-        }
-      }
-      counter += str->length();
-    }
-  }
   DCHECK(!storage || storage->length() == counter);
   return counter;
 }