Pre-create properties on JSRegExp objects

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index 01977f0929d8fc1babcc3272aebf63381e2a4f30..d299d92a25737d74e6a86b2000994dabb8de0709 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -3667,6 +3667,13 @@ class JSRegExp: public JSObject {
       FixedArray::kHeaderSize + kIrregexpUC16CodeIndex * kPointerSize;
   static const int kIrregexpCaptureCountOffset =
       FixedArray::kHeaderSize + kIrregexpCaptureCountIndex * kPointerSize;
+
+  // In-object fields.
+  static const int kSourceFieldIndex = 0;
+  static const int kGlobalFieldIndex = 1;
+  static const int kIgnoreCaseFieldIndex = 2;
+  static const int kMultilineFieldIndex = 3;
+  static const int kLastIndexFieldIndex = 4;
 };