Revert of Simplify and compact transitions storage

src/heap-snapshot-generator.cc

Index: src/heap-snapshot-generator.cc
diff --git a/src/heap-snapshot-generator.cc b/src/heap-snapshot-generator.cc
index 2809072c9c9521aa21a96666d17da24cfd94ed3c..6fb68702fdc2a28ca2e02a783c1b2b6f3a19b58c 100644
--- a/src/heap-snapshot-generator.cc
+++ b/src/heap-snapshot-generator.cc
@@ -1286,30 +1286,27 @@
 
 
 void V8HeapExplorer::ExtractMapReferences(int entry, Map* map) {
-  Object* raw_transitions = map->raw_transitions();
-  if (TransitionArray::IsFullTransitionArray(raw_transitions)) {
-    TransitionArray* transitions = TransitionArray::cast(raw_transitions);
+  if (map->HasTransitionArray()) {
+    TransitionArray* transitions = map->transitions();
     int transitions_entry = GetEntry(transitions)->index();
 
     if (FLAG_collect_maps && map->CanTransition()) {
-      if (transitions->HasPrototypeTransitions()) {
-        FixedArray* prototype_transitions =
-            transitions->GetPrototypeTransitions();
-        MarkAsWeakContainer(prototype_transitions);
-        TagObject(prototype_transitions, "(prototype transitions");
-        SetInternalReference(transitions, transitions_entry,
-                             "prototype_transitions", prototype_transitions);
+      if (!transitions->IsSimpleTransition()) {
+        if (transitions->HasPrototypeTransitions()) {
+          FixedArray* prototype_transitions =
+              transitions->GetPrototypeTransitions();
+          MarkAsWeakContainer(prototype_transitions);
+          TagObject(prototype_transitions, "(prototype transitions");
+          SetInternalReference(transitions, transitions_entry,
+                               "prototype_transitions", prototype_transitions);
+        }
+        // TODO(alph): transitions keys are strong links.
+        MarkAsWeakContainer(transitions);
       }
-      // TODO(alph): transitions keys are strong links.
-      MarkAsWeakContainer(transitions);
     }
 
     TagObject(transitions, "(transition array)");
     SetInternalReference(map, entry, "transitions", transitions,
-                         Map::kTransitionsOffset);
-  } else if (TransitionArray::IsSimpleTransition(raw_transitions)) {
-    TagObject(raw_transitions, "(transition)");
-    SetInternalReference(map, entry, "transition", raw_transitions,
                          Map::kTransitionsOffset);
   }
   DescriptorArray* descriptors = map->instance_descriptors();