[serializer] Add API to warm up startup snapshot with an additional script.

src/snapshot/partial-serializer.cc

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/snapshot/partial-serializer.h"
 
 #include "src/objects-inl.h"
 
 namespace v8 {
 namespace internal {
 
 PartialSerializer::PartialSerializer(Isolate* isolate,
                                      Serializer* startup_snapshot_serializer,
                                      SnapshotByteSink* sink)
     : Serializer(isolate, sink),
       startup_serializer_(startup_snapshot_serializer),
-      global_object_(NULL) {
+      global_object_(NULL),
+      next_partial_cache_index_(0) {
   InitializeCodeAddressMap();
 }
 
 PartialSerializer::~PartialSerializer() {
   OutputStatistics("PartialSerializer");
 }
 
 void PartialSerializer::Serialize(Object** o) {
   if ((*o)->IsContext()) {
     Context* context = Context::cast(*o);
@@ skipping 59 matching lines @@
     FixedArray* literals = JSFunction::cast(obj)->literals();
     for (int i = 0; i < literals->length(); i++) literals->set_undefined(i);
   }
 
   // Object has not yet been serialized.  Serialize it here.
   ObjectSerializer serializer(this, obj, sink_, how_to_code, where_to_point);
   serializer.Serialize();
 }
 
 int PartialSerializer::PartialSnapshotCacheIndex(HeapObject* heap_object) {
-  Isolate* isolate = this->isolate();
-  List<Object*>* cache = isolate->partial_snapshot_cache();
-  int new_index = cache->length();
-
-  int index = partial_cache_index_map_.LookupOrInsert(heap_object, new_index);
+  int index = partial_cache_index_map_.LookupOrInsert(
+      heap_object, next_partial_cache_index_);
   if (index == PartialCacheIndexMap::kInvalidIndex) {
-    // We didn't find the object in the cache.  So we add it to the cache and
-    // then visit the pointer so that it becomes part of the startup snapshot
-    // and we can refer to it from the partial snapshot.
-    cache->Add(heap_object);
+    // This object is not part of the partial snapshot cache yet. Add it to the
+    // startup snapshot so we can refer to it via partial snapshot index from
+    // the partial snapshot.
     startup_serializer_->VisitPointer(reinterpret_cast<Object**>(&heap_object));
-    // We don't recurse from the startup snapshot generator into the partial
-    // snapshot generator.
-    return new_index;
+    return next_partial_cache_index_++;
   }
   return index;
 }
 
 bool PartialSerializer::ShouldBeInThePartialSnapshotCache(HeapObject* o) {
   // Scripts should be referred only through shared function infos.  We can't
   // allow them to be part of the partial snapshot because they contain a
   // unique ID, and deserializing several partial snapshots containing script
   // would cause dupes.
   DCHECK(!o->IsScript());
   return o->IsName() || o->IsSharedFunctionInfo() || o->IsHeapNumber() ||
          o->IsCode() || o->IsScopeInfo() || o->IsAccessorInfo() ||
          o->map() ==
              startup_serializer_->isolate()->heap()->fixed_cow_array_map();
 }
 
 }  // namespace internal
 }  // namespace v8