Add a premonomorphic state to the call target cache.

src/objects.h

Index: src/objects.h
===================================================================
--- src/objects.h	(revision 19345)
+++ src/objects.h	(working copy)
@@ -8180,6 +8180,9 @@
   // The object that indicates an uninitialized cache.
   static inline Handle<Object> UninitializedSentinel(Isolate* isolate);
 
+  // The object that indicates a cache in pre-monomorphic state.
+  static inline Handle<Object> PremonomorphicSentinel(Isolate* isolate);
+
   // The object that indicates a megamorphic state.
   static inline Handle<Object> MegamorphicSentinel(Isolate* isolate);