Make ClassFinalizer indifferent on whether we are generating a snapshot or not.

runtime/vm/snapshot.cc

Index: runtime/vm/snapshot.cc
===================================================================
--- runtime/vm/snapshot.cc	(revision 11197)
+++ runtime/vm/snapshot.cc	(working copy)
@@ -534,6 +534,16 @@
 }
 
 
+RawApiError* SnapshotReader::NewApiError() {
+  ALLOC_NEW_OBJECT(ApiError, Object::api_error_class());
+}
+
+
+RawLanguageError* SnapshotReader::NewLanguageError() {
+  ALLOC_NEW_OBJECT(LanguageError, Object::language_error_class());
+}
+
+
 RawClass* SnapshotReader::LookupInternalClass(intptr_t class_header) {
   // If the header is an object Id, lookup singleton VM classes or classes
   // stored in the object store.