Simplify type argument instantiation cache lookup by introducing an array

runtime/vm/raw_object_snapshot.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/bigint_operations.h"
 #include "vm/object.h"
 #include "vm/object_store.h"
 #include "vm/snapshot.h"
 #include "vm/symbols.h"
 #include "vm/visitor.h"
@@ skipping 435 matching lines @@
 
   TypeArguments& type_arguments = TypeArguments::ZoneHandle(
       reader->isolate(), NEW_OBJECT_WITH_LEN_SPACE(TypeArguments, len, kind));
   reader->AddBackRef(object_id, &type_arguments, kIsDeserialized);
 
   // Set the instantiations field, which is only read from a full snapshot.
   if (kind == Snapshot::kFull) {
     *reader->ArrayHandle() ^= reader->ReadObjectImpl();
     type_arguments.set_instantiations(*reader->ArrayHandle());
   } else {
-    // TODO(regis): Change to Object::zero_array() once supported.
-    type_arguments.set_instantiations(Object::empty_array());
+    type_arguments.set_instantiations(Object::zero_array());
   }
 
   // Now set all the type fields.
   for (intptr_t i = 0; i < len; i++) {
     *reader->TypeHandle() ^= reader->ReadObjectImpl();
     type_arguments.set_type_at(i, *reader->TypeHandle());
   }
 
   // If object needs to be a canonical object, Canonicalize it.
   // When reading a full snapshot we don't need to canonicalize the object
@@ skipping 2208 matching lines @@
     // We do not allow objects with native fields in an isolate message.
     writer->SetWriteException(Exceptions::kArgument,
                               "Illegal argument in isolate message"
                               " : (object is a MirrorReference)");
   } else {
     UNREACHABLE();
   }
 }
 
 }  // namespace dart