Revert "Inobject slack tracking is done on a per-closure basis instead of per-shared info basis."

src/mark-compact.cc

Index: src/mark-compact.cc
diff --git a/src/mark-compact.cc b/src/mark-compact.cc
index ce4d6ac655887e638848ca06229502e20e6f3deb..b857c793798a4f91a8f87ff9830acf465f9898a5 100644
--- a/src/mark-compact.cc
+++ b/src/mark-compact.cc
@@ -417,6 +417,8 @@ void MarkCompactCollector::CollectGarbage() {
 
   SweepSpaces();
 
+  if (!FLAG_collect_maps) ReattachInitialMaps();
+
 #ifdef DEBUG
   if (FLAG_verify_native_context_separation) {
     VerifyNativeContextSeparation(heap_);
@@ -2532,6 +2534,23 @@ void MarkCompactCollector::ProcessMapCaches() {
 }
 
 
+void MarkCompactCollector::ReattachInitialMaps() {
+  HeapObjectIterator map_iterator(heap()->map_space());
+  for (HeapObject* obj = map_iterator.Next();
+       obj != NULL;
+       obj = map_iterator.Next()) {
+    Map* map = Map::cast(obj);
+
+    STATIC_ASSERT(LAST_TYPE == LAST_JS_RECEIVER_TYPE);
+    if (map->instance_type() < FIRST_JS_RECEIVER_TYPE) continue;
+
+    if (map->attached_to_shared_function_info()) {
+      JSFunction::cast(map->constructor())->shared()->AttachInitialMap(map);
+    }
+  }
+}
+
+
 void MarkCompactCollector::ClearNonLiveReferences() {
   // Iterate over the map space, setting map transitions that go from
   // a marked map to an unmarked map to null transitions.  This action
@@ -2545,6 +2564,13 @@ void MarkCompactCollector::ClearNonLiveReferences() {
     if (!map->CanTransition()) continue;
 
     MarkBit map_mark = Marking::MarkBitFrom(map);
+    if (map_mark.Get() && map->attached_to_shared_function_info()) {
+      // This map is used for inobject slack tracking and has been detached
+      // from SharedFunctionInfo during the mark phase.
+      // Since it survived the GC, reattach it now.
+      JSFunction::cast(map->constructor())->shared()->AttachInitialMap(map);
+    }
+
     ClearNonLivePrototypeTransitions(map);
     ClearNonLiveMapTransitions(map, map_mark);