Replace HeapType with a non-templated FieldType class.

src/lookup.cc

Index: src/lookup.cc
diff --git a/src/lookup.cc b/src/lookup.cc
index 48da4fabeea4eff3db524976b3e177bc1b5c8aab..c19e25c024c91541dddc7bb7d506f965e97c50dc 100644
--- a/src/lookup.cc
+++ b/src/lookup.cc
@@ -476,8 +476,7 @@ FieldIndex LookupIterator::GetFieldIndex() const {
   return FieldIndex::ForPropertyIndex(*holder_map_, index, is_double);
 }
 
-
-Handle<HeapType> LookupIterator::GetFieldType() const {
+Handle<FieldType> LookupIterator::GetFieldType() const {
   DCHECK(has_property_);
   DCHECK(!holder_map_->is_dictionary_map());
   DCHECK_EQ(v8::internal::DATA, property_details_.type());