Fix bug where strings were not flattened before regexp.

src/objects-inl.h

Index: src/objects-inl.h
===================================================================
--- src/objects-inl.h	(revision 1138)
+++ src/objects-inl.h	(working copy)
@@ -1431,13 +1431,14 @@
 }
 
 
-void String::TryFlatten(StringShape shape) {
+Object* String::TryFlattenIfNotFlat(StringShape shape) {
   ASSERT(shape.type() == StringShape(this).type());
   // We don't need to flatten strings that are already flat.  Since this code
   // is inlined, it can be helpful in the flat case to not call out to Flatten.
   if (!IsFlat(shape)) {
-    Flatten(shape);
+    return TryFlatten(shape);
   }
+  return this;
 }