One instead of two runtime calls when initializing regexp.

src/jsregexp.h

Index: src/jsregexp.h
diff --git a/src/jsregexp.h b/src/jsregexp.h
index c65adea4c5cf04d6e92f02642b4eb7ee44fa36df..8c02e71183df4e8f410ea95b829167bc6ee793f4 100644
--- a/src/jsregexp.h
+++ b/src/jsregexp.h
@@ -46,10 +46,9 @@ class RegExpImpl {
   // generic data and choice of implementation - as well as what
   // the implementation wants to store in the data field.
   // Returns false if compilation fails.
-  MUST_USE_RESULT static MaybeHandle<Object> Compile(
-      Handle<JSRegExp> re,
-      Handle<String> pattern,
-      Handle<String> flags);
+  MUST_USE_RESULT static MaybeHandle<Object> Compile(Handle<JSRegExp> re,
+                                                     Handle<String> pattern,
+                                                     JSRegExp::Flags flags);
 
   // See ECMA-262 section 15.10.6.2.
   // This function calls the garbage collector if necessary.