Use in-object fields instead of private symbols for regexp slots.

src/runtime/runtime.h

Index: src/runtime/runtime.h
diff --git a/src/runtime/runtime.h b/src/runtime/runtime.h
index 872cf1194dae3f0a574596a9c7cb6b04e0c9e0aa..96c2c1c7618cb5eb173f1a4e64e6e1a820ef13ce 100644
--- a/src/runtime/runtime.h
+++ b/src/runtime/runtime.h
@@ -559,6 +559,8 @@ namespace internal {
   F(StringReplaceGlobalRegExpWithString, 4, 1) \
   F(StringSplit, 3, 1)                         \
   F(RegExpExec, 4, 1)                          \
+  F(RegExpFlags, 1, 1)                         \
+  F(RegExpSource, 1, 1)                        \
   F(RegExpConstructResult, 3, 1)               \
   F(RegExpInitializeAndCompile, 3, 1)          \
   F(MaterializeRegExpLiteral, 4, 1)            \