Ensure that all non-stable maps created by Map::AddMissingTransitions() are marked as such.

test/cctest/test-field-type-tracking.cc

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <stdlib.h>
 #include <utility>
 
 #include "test/cctest/test-api.h"
 
 #include "src/v8.h"
@@ skipping 603 matching lines @@
     CHECK(!info.dependencies()->HasAborted());
 
   } else {
     CHECK(!field_owner->is_deprecated());
     CHECK(map->is_stable());  // Map did not change, must be left stable.
     CHECK_EQ(*map, *new_map);
 
     CHECK_EQ(expected_field_type_dependency, info.dependencies()->HasAborted());
   }
 
+  {
+    // Check that all previous maps are not stable.
+    Map* tmp = *new_map;
+    while (true) {
+      Object* back = tmp->GetBackPointer();
+      if (back->IsUndefined()) break;
+      tmp = Map::cast(back);
+      CHECK(!tmp->is_stable());
+    }
+  }
+
   info.dependencies()->Rollback();  // Properly cleanup compilation info.
 
   // Update all deprecated maps and check that they are now the same.
   Handle<Map> updated_map = Map::Update(map);
   CHECK_EQ(*new_map, *updated_map);
 }
 
 
 static void TestGeneralizeRepresentation(
     Representation from_representation, Handle<HeapType> from_type,
@@ skipping 1545 matching lines @@
   Handle<AccessorPair> pair = CreateAccessorPair(true, true);
   TransitionToAccessorConstantOperator transition_op(pair);
 
   SameMapChecker checker;
   TestTransitionTo(transition_op, transition_op, checker);
 }
 
 
 // TODO(ishell): add this test once IS_ACCESSOR_FIELD_SUPPORTED is supported.
 // TEST(TransitionAccessorConstantToAnotherAccessorConstant)