Use hash map to look for objects in the root array when serializing.

src/heap/heap-inl.h

Index: src/heap/heap-inl.h
diff --git a/src/heap/heap-inl.h b/src/heap/heap-inl.h
index e658224aca11190003676d9bbd2df945e1c88508..9e3421e3220fdd8606cfe2f3445f92b91f3f97d9 100644
--- a/src/heap/heap-inl.h
+++ b/src/heap/heap-inl.h
@@ -699,7 +699,7 @@ void ExternalStringTable::ShrinkNewStrings(int position) {
 
 
 void Heap::ClearInstanceofCache() {
-  set_instanceof_cache_function(the_hole_value());
+  set_instanceof_cache_function(Smi::FromInt(0));
 }
 
 
@@ -709,8 +709,8 @@ Object* Heap::ToBoolean(bool condition) {
 
 
 void Heap::CompletelyClearInstanceofCache() {
-  set_instanceof_cache_map(the_hole_value());
-  set_instanceof_cache_function(the_hole_value());
+  set_instanceof_cache_map(Smi::FromInt(0));
+  set_instanceof_cache_function(Smi::FromInt(0));
 }