Use direct copy and templates to speed up flattening of strings.

src/objects-inl.h

Index: src/objects-inl.h
===================================================================
--- src/objects-inl.h	(revision 535)
+++ src/objects-inl.h	(working copy)
@@ -1369,6 +1369,12 @@
 }
 
 
+int String::full_representation_tag() {

[Christian Plesner Hansen, 2008/10/21 14:16:22]

We have a lot of these methods with lower-case names that do nontrivial work. 
We have to be sure they're really fast, otherwise we should rename them to upper
camel case names.

[Erik Corry, 2008/10/22 11:59:48]

This one is certainly trivial.

+  return map()->instance_type() &
+         (kStringRepresentationMask | kStringEncodingMask);
+}
+
+
 StringRepresentationTag String::representation_tag() {
   return map_representation_tag(map());
 }