[snapshot] introduce SnapshotCreator API.

src/heap/heap.cc

Index: src/heap/heap.cc
diff --git a/src/heap/heap.cc b/src/heap/heap.cc
index f830b4dd1bcfaf26a5a743a250f9bdef2ed3c522..9a6b3229def2f1657f27dec9e666e07db5c1e7de 100644
--- a/src/heap/heap.cc
+++ b/src/heap/heap.cc
@@ -5610,6 +5610,25 @@ DependentCode* Heap::LookupWeakObjectToCodeDependency(Handle<HeapObject> obj) {
   return DependentCode::cast(empty_fixed_array());
 }
 
+void Heap::CompactWeakFixedArrays() {
+  // Find known WeakFixedArrays and compact them.
+  i::HeapIterator iterator(this);
+  for (i::HeapObject* o = iterator.next(); o != NULL; o = iterator.next()) {
+    if (o->IsPrototypeInfo()) {
+      i::Object* prototype_users = i::PrototypeInfo::cast(o)->prototype_users();
+      if (prototype_users->IsWeakFixedArray()) {
+        i::WeakFixedArray* array = i::WeakFixedArray::cast(prototype_users);
+        array->Compact<i::JSObject::PrototypeRegistryCompactionCallback>();
+      }
+    } else if (o->IsScript()) {
+      i::Object* shared_list = i::Script::cast(o)->shared_function_infos();
+      if (shared_list->IsWeakFixedArray()) {
+        i::WeakFixedArray* array = i::WeakFixedArray::cast(shared_list);
+        array->Compact<i::WeakFixedArray::NullCallback>();
+      }
+    }
+  }
+}
 
 void Heap::AddRetainedMap(Handle<Map> map) {
   Handle<WeakCell> cell = Map::WeakCellForMap(map);