Do not mark prototype transitions link as weak in heap snapshot.

R=ulan@chromium.org

Review URL: https://codereview.chromium.org/223643004

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@20490 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/heap-snapshot-generator.cc

@@ -1322,8 +1322,23 @@ void V8HeapExplorer::ExtractMapReferences(int entry, Map* map) {
     TagObject(back_pointer, "(back pointer)");
     SetInternalReference(transitions, transitions_entry,
                          "back_pointer", back_pointer);
+
+    if (FLAG_collect_maps && map->CanTransition()) {
+      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);
+      }
+    }
+
     TagObject(transitions, "(transition array)");
-    MarkAsWeakContainer(transitions);
     SetInternalReference(map, entry,
                          "transitions", transitions,
                          Map::kTransitionsOrBackPointerOffset);