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

src/crankshaft/hydrogen.cc

Index: src/crankshaft/hydrogen.cc
diff --git a/src/crankshaft/hydrogen.cc b/src/crankshaft/hydrogen.cc
index cfd843bfdc984de64fbd8b6e63faf5bf6319dc54..c71fa6b42d705061bba12781c6d27ac10ebef8ae 100644
--- a/src/crankshaft/hydrogen.cc
+++ b/src/crankshaft/hydrogen.cc
@@ -12644,6 +12644,16 @@ void HOptimizedGraphBuilder::GenerateRegExpExec(CallRuntime* call) {
 }
 
 
+void HOptimizedGraphBuilder::GenerateRegExpFlags(CallRuntime* call) {
+  DCHECK_EQ(1, call->arguments()->length());
+  CHECK_ALIVE(VisitExpressions(call->arguments()));
+  HValue* regexp = Pop();
+  HValue* result =
+      New<HLoadNamedField>(regexp, nullptr, HObjectAccess::ForJSRegExpFlags());
+  return ast_context()->ReturnInstruction(result, call->id());
+}
+
+
 void HOptimizedGraphBuilder::GenerateDoubleLo(CallRuntime* call) {
   DCHECK_EQ(1, call->arguments()->length());
   CHECK_ALIVE(VisitForValue(call->arguments()->at(0)));