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

src/bootstrapper.cc

Index: src/bootstrapper.cc
diff --git a/src/bootstrapper.cc b/src/bootstrapper.cc
index 0e0cd78b1891f9af197d37c385f3247be377eac1..d69ab5b1c9657a9aa744ca74fab8c8d4c2250eff 100644
--- a/src/bootstrapper.cc
+++ b/src/bootstrapper.cc
@@ -1223,32 +1223,15 @@ void Genesis::InitializeGlobal(Handle<JSGlobalObject> global_object,
 
     DCHECK_EQ(0, initial_map->GetInObjectProperties());
 
-    PropertyAttributes final =
-        static_cast<PropertyAttributes>(DONT_ENUM | DONT_DELETE | READ_ONLY);
-    Map::EnsureDescriptorSlack(initial_map, 5);
+    Map::EnsureDescriptorSlack(initial_map, 1);
 
-    {
-      // ES6 21.2.3.2.1
-      DataDescriptor field(factory->regexp_source_symbol(),
-                           JSRegExp::kSourceFieldIndex, final,
-                           Representation::Tagged());
-      initial_map->AppendDescriptor(&field);
-    }
-    {
-      DataDescriptor field(factory->regexp_flags_symbol(),
-                           JSRegExp::kFlagsFieldIndex, final,
-                           Representation::Smi());
-      initial_map->AppendDescriptor(&field);
-    }
-    {
-      // ECMA-262, section 15.10.7.5.
-      PropertyAttributes writable =
-          static_cast<PropertyAttributes>(DONT_ENUM | DONT_DELETE);
-      DataDescriptor field(factory->last_index_string(),
-                           JSRegExp::kLastIndexFieldIndex, writable,
-                           Representation::Tagged());
-      initial_map->AppendDescriptor(&field);
-    }
+    // ECMA-262, section 15.10.7.5.
+    PropertyAttributes writable =
+        static_cast<PropertyAttributes>(DONT_ENUM | DONT_DELETE);
+    DataDescriptor field(factory->last_index_string(),
+                         JSRegExp::kLastIndexFieldIndex, writable,
+                         Representation::Tagged());
+    initial_map->AppendDescriptor(&field);
 
     static const int num_fields = JSRegExp::kInObjectFieldCount;
     initial_map->SetInObjectProperties(num_fields);