Implement LookupIterator designed to replace LookupResult

src/handles.h

Index: src/handles.h
diff --git a/src/handles.h b/src/handles.h
index 19e023b7a8f046c06312e2572fdd063a14901c28..3bd82e51e3a542d023d146e067c4c5e146d1539f 100644
--- a/src/handles.h
+++ b/src/handles.h
@@ -44,10 +44,10 @@ class MaybeHandle {
     location_ = reinterpret_cast<T**>(maybe_handle.location_);
   }
 
-  INLINE(void Assert()) { ASSERT(location_ != NULL); }
-  INLINE(void Check()) { CHECK(location_ != NULL); }
+  INLINE(void Assert() const) { ASSERT(location_ != NULL); }
+  INLINE(void Check() const) { CHECK(location_ != NULL); }
 
-  INLINE(Handle<T> ToHandleChecked()) {
+  INLINE(Handle<T> ToHandleChecked()) const {
     Check();
     return Handle<T>(location_);
   }