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

src/crankshaft/hydrogen-instructions.cc

Index: src/crankshaft/hydrogen-instructions.cc
diff --git a/src/crankshaft/hydrogen-instructions.cc b/src/crankshaft/hydrogen-instructions.cc
index 7417c1b898cede6b47d886adbb5a472b3f7cac1d..47665f4b6e28b449630e047dc02d1794889346ff 100644
--- a/src/crankshaft/hydrogen-instructions.cc
+++ b/src/crankshaft/hydrogen-instructions.cc
@@ -1650,6 +1650,9 @@ void HCheckInstanceType::GetCheckInterval(InstanceType* first,
     case IS_JS_DATE:
       *first = *last = JS_DATE_TYPE;
       return;
+    case IS_JS_REGEXP:
+      *first = *last = JS_REGEXP_TYPE;
+      return;
     default:
       UNREACHABLE();
   }
@@ -1719,8 +1722,8 @@ const char* HCheckInstanceType::GetCheckName() const {
   switch (check_) {
     case IS_SPEC_OBJECT: return "object";
     case IS_JS_ARRAY: return "array";
-    case IS_JS_DATE:
-      return "date";
+    case IS_JS_DATE: return "date";
+    case IS_JS_REGEXP: return "regexp";
     case IS_STRING: return "string";
     case IS_INTERNALIZED_STRING: return "internalized_string";
   }