Setup a peer for read only strings that are not externalized in

runtime/include/dart_api.h

Index: runtime/include/dart_api.h
===================================================================
--- runtime/include/dart_api.h	(revision 26385)
+++ runtime/include/dart_api.h	(working copy)
@@ -1410,12 +1410,6 @@
                                                 intptr_t length);
 
 /**
- * Retrieves the peer pointer associated with an external String.
- */
-DART_EXPORT Dart_Handle Dart_ExternalStringGetPeer(Dart_Handle object,
-                                                   void** peer);
-
-/**
  * Returns a String which references an external array of
  * Latin-1 (ISO-8859-1) encoded characters.
  *
@@ -1536,8 +1530,9 @@
  * \return the converted ExternalString object if no error occurs.
  *   Otherwise returns an error handle.
  *   If the object is a valid string but if it cannot be externalized
- *   then Dart_Null() is returned and the string data is copied into
- *   the external space specified.
+ *   the string data is copied into the external space specified
+ *   and the passed in peer is setup as a peer for this string object.
+ *   In this case the function returns the original String object as is.
  *
  * For example:
  *  intptr_t size;