[ic] Use UnseededNumberDictionary as a storage for names in TypeFeedbackMetadata.

src/type-info.cc

Index: src/type-info.cc
diff --git a/src/type-info.cc b/src/type-info.cc
index 5f5c1e87311661cb95c24bd6e27a05daa290f480..61af125c47c22f7fa9ead72f69b4be9a4cab67d6 100644
--- a/src/type-info.cc
+++ b/src/type-info.cc
@@ -20,7 +20,7 @@ TypeFeedbackOracle::TypeFeedbackOracle(
     Handle<TypeFeedbackVector> feedback_vector, Handle<Context> native_context)
     : native_context_(native_context), isolate_(isolate), zone_(zone) {
   BuildDictionary(code);
-  DCHECK(dictionary_->IsDictionary());
+  DCHECK(dictionary_->IsUnseededNumberDictionary());
   // We make a copy of the feedback vector because a GC could clear
   // the type feedback info contained therein.
   // TODO(mvstanton): revisit the decision to copy when we weakly