Landing http://codereview.chromium.org/1594017 for Ryan.

include/v8.h

Index: include/v8.h
diff --git a/include/v8.h b/include/v8.h
index d4a323f0144d25eab1497ed6c89a84548a72bb2b..db739bb7b68feb10e4280bd9ad246262bf365933 100644
--- a/include/v8.h
+++ b/include/v8.h
@@ -866,6 +866,13 @@ class V8EXPORT String : public Primitive {
                 int* nchars_ref = NULL) const; // UTF-8
 
   /**
+   * Flatten internal memory. Operations on the string tend to run faster
+   * after flattening especially if the string is a concatenation of many
+   * others.
+   */
+  void Flatten();
+
+  /**
    * A zero length string.
    */
   static v8::Local<v8::String> Empty();