Retain maps embedded in optimized code for several garbage collections.

src/heap/heap.cc

Index: src/heap/heap.cc
diff --git a/src/heap/heap.cc b/src/heap/heap.cc
index 26cffc8fb5524e51310776f74c2fbc3e0e7edf8b..978920ff01d8da694ae9fd37c11a5a9f0a9e3a58 100644
--- a/src/heap/heap.cc
+++ b/src/heap/heap.cc
@@ -915,6 +915,7 @@ int Heap::NotifyContextDisposed(bool dependant_context) {
   if (!dependant_context) {
     tracer()->ResetSurvivalEvents();
     old_generation_size_configured_ = false;
+    set_retained_maps(ArrayList::cast(empty_fixed_array()));
   }
   if (isolate()->concurrent_recompilation_enabled()) {
     // Flush the queued recompilation tasks.
@@ -3107,6 +3108,7 @@ void Heap::CreateInitialObjects() {
   }
 
   set_detached_contexts(empty_fixed_array());
+  set_retained_maps(ArrayList::cast(empty_fixed_array()));
 
   set_weak_object_to_code_table(
       *WeakHashTable::New(isolate(), 16, USE_DEFAULT_MINIMUM_CAPACITY,
@@ -5747,6 +5749,18 @@ DependentCode* Heap::LookupWeakObjectToCodeDependency(Handle<HeapObject> obj) {
 }
 
 
+void Heap::AddRetainedMap(Handle<Map> map) {
+  if (FLAG_retain_maps_for_n_gc == 0) return;
+  Handle<WeakCell> cell = Map::WeakCellForMap(map);
+  Handle<ArrayList> array(retained_maps(), isolate());
+  array = ArrayList::Add(
+      array, cell, handle(Smi::FromInt(FLAG_retain_maps_for_n_gc), isolate()));
+  if (*array != retained_maps()) {
+    set_retained_maps(*array);
+  }
+}
+
+
 void Heap::FatalProcessOutOfMemory(const char* location, bool take_snapshot) {
   v8::internal::V8::FatalProcessOutOfMemory(location, take_snapshot);
 }