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

test/cctest/test-unboxed-doubles.cc

 // Copyright 2014 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 "src/v8.h"
 
 #include "src/compilation-cache.h"
@@ skipping 741 matching lines @@
   // This method calls LayoutDescriptor::AppendIfFastOrUseFull() internally
   // and does all the required map-descriptors related book keeping.
   Handle<Map> last_map = Map::AddMissingTransitionsForTesting(
       initial_map, descriptors, full_layout_descriptor);
 
   // Follow back pointers to construct a sequence of maps from |map|
   // to |last_map|.
   int descriptors_length = descriptors->number_of_descriptors();
   std::vector<Handle<Map>> maps(descriptors_length);
   {
+    CHECK(last_map->is_stable());
     Map* map = *last_map;
     for (int i = 0; i < descriptors_length; i++) {
       maps[descriptors_length - 1 - i] = handle(map, isolate);
       Object* maybe_map = map->GetBackPointer();
       CHECK(maybe_map->IsMap());
       map = Map::cast(maybe_map);
+      CHECK(!map->is_stable());
     }
     CHECK_EQ(1, maps[0]->NumberOfOwnDescriptors());
   }
 
   Handle<Map> map;
   // Now check layout descriptors of all intermediate maps.
   for (int i = 0; i < number_of_descriptors; i++) {
     PropertyDetails details = descriptors->GetDetails(i);
     map = maps[i];
     LayoutDescriptor* layout_desc = map->layout_descriptor();
@@ skipping 842 matching lines @@
 
 // TODO(ishell): add respective tests for property kind reconfiguring from
 // accessor field to double, once accessor fields are supported by
 // Map::ReconfigureProperty().
 
 
 // TODO(ishell): add respective tests for fast property removal case once
 // Map::ReconfigureProperty() supports that.
 
 #endif