[ic] Split megamorphic stub cache in two caches (for loads and for stores).

src/ic/ic.h

Index: src/ic/ic.h
diff --git a/src/ic/ic.h b/src/ic/ic.h
index 72c47db4fc988906a8641cc3a0d621ad35defed7..088ca84779b9adc5a9745e9192bf61a61b151ac3 100644
--- a/src/ic/ic.h
+++ b/src/ic/ic.h
@@ -153,6 +153,8 @@ class IC {
   bool UpdatePolymorphicIC(Handle<Name> name, Handle<Code> code);
   void UpdateMegamorphicCache(Map* map, Name* name, Code* code);
 
+  StubCache* stub_cache();
+
   void CopyICToMegamorphicCache(Handle<Name> name);
   bool IsTransitionOfMonomorphicTarget(Map* source_map, Map* target_map);
   void PatchCache(Handle<Name> name, Handle<Code> code);