Update subclasses array and is_implemented bit when loading script snapshots.

runtime/vm/snapshot.h

Index: runtime/vm/snapshot.h
diff --git a/runtime/vm/snapshot.h b/runtime/vm/snapshot.h
index d6e787223a73f924240c24130d4d2c243d58130f..faf5eede693711054ff4fa18546ddef098c3cbc5 100644
--- a/runtime/vm/snapshot.h
+++ b/runtime/vm/snapshot.h
@@ -446,6 +446,10 @@ class SnapshotReader : public BaseReader {
   // Process all the deferred canonicalization entries and patch all references.
   void ProcessDeferredCanonicalizations();
 
+  // Update subclasses array and is implemented bit for interfaces/superclass in
+  // the core snapshot.
+  void FixSubclassesAndImplementors();
+
   // Decode class id from the header field.
   intptr_t LookupInternalClass(intptr_t class_header);