Only remove the code object that caused the monomorphic prototype...

src/objects.h

Index: src/objects.h
===================================================================
--- src/objects.h	(revision 313)
+++ src/objects.h	(working copy)
@@ -2343,9 +2343,13 @@
   // Returns the found code or undefined if absent.
   Object* FindInCodeCache(String* name, Code::Flags flags);
 
-  // Tells whether code is in the code cache.
-  bool IncludedInCodeCache(Code* code);
+  // Returns the non-negative index of the code object if it is in the
+  // cache and -1 otherwise.
+  int IndexInCodeCache(Code* code);
 
+  // Removes a code object from the code cache at the given index.
+  void RemoveFromCodeCache(int index);
+
   // Dispatched behavior.
   void MapIterateBody(ObjectVisitor* v);
 #ifdef DEBUG