Optimize ClearNonLiveReferences: do not compact prototype transitions in GC.

src/transitions.h

Index: src/transitions.h
diff --git a/src/transitions.h b/src/transitions.h
index 1fcd3860d0bdc552490d42d00a84e97d41dbf26b..72356beb2ee733232a6a88d710ff73699bd1f580 100644
--- a/src/transitions.h
+++ b/src/transitions.h
@@ -102,6 +102,9 @@ class TransitionArray: public FixedArray {
   static const int kMaxCachedPrototypeTransitions = 256;
   static void PutPrototypeTransition(Handle<Map> map, Handle<Object> prototype,
                                      Handle<Map> target_map);
+  static bool CompactPrototypeTransitionArray(FixedArray* array);
+  static Handle<FixedArray> GrowPrototypeTransitionArray(
+      Handle<FixedArray> array, int new_capacity, Isolate* isolate);
 
   static Handle<Map> GetPrototypeTransition(Handle<Map> map,
                                             Handle<Object> prototype);