Inline relevant parts of MigrateToMap into AllocateStorageForMap

This speeds up the json parser by 10-20%

Bug: chromium:771227
Change-Id: Ib2392471bdd9ff9041237708cb272229b5ece410
Reviewed-on: https://chromium-review.googlesource.com/700494
Commit-Queue: Toon Verwaest <verwaest@chromium.org>
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48287}

src/objects.cc

@@ -5826,7 +5826,55 @@ void JSObject::AllocateStorageForMap(Handle<JSObject> object, Handle<Map> map) {
     }
     map = Map::ReconfigureElementsKind(map, to_kind);
   }
-  JSObject::MigrateToMap(object, map);
+  int number_of_fields = map->NumberOfFields();
+  int inobject = map->GetInObjectProperties();
+  int unused = map->unused_property_fields();
+  int total_size = number_of_fields + unused;
+  int external = total_size - inobject;
+  // Allocate mutable double boxes if necessary. It is always necessary if we
+  // have external properties, but is also necessary if we only have inobject
+  // properties but don't unbox double fields.
+  if (!FLAG_unbox_double_fields || external > 0) {
+    Isolate* isolate = object->GetIsolate();
+
+    Handle<DescriptorArray> descriptors(map->instance_descriptors());
+    Handle<FixedArray> storage;
+    if (!FLAG_unbox_double_fields) {
+      storage = isolate->factory()->NewFixedArray(inobject);
+    }
+
+    Handle<PropertyArray> array;
+    if (external > 0) {
+      array = isolate->factory()->NewPropertyArray(external);
+    }
+
+    for (int i = 0; i < map->NumberOfOwnDescriptors(); i++) {
+      PropertyDetails details = descriptors->GetDetails(i);
+      Representation representation = details.representation();
+      if (!representation.IsDouble()) continue;
+      FieldIndex index = FieldIndex::ForDescriptor(*map, i);
+      if (map->IsUnboxedDoubleField(index)) continue;
+      Handle<HeapNumber> box = isolate->factory()->NewMutableHeapNumber();
+      if (index.is_inobject()) {
+        storage->set(index.property_index(), *box);
+      } else {
+        array->set(index.outobject_array_index(), *box);
+      }
+    }
+
+    if (external > 0) {
+      object->SetProperties(*array);
+    }
+
+    if (!FLAG_unbox_double_fields) {
+      for (int i = 0; i < inobject; i++) {
+        FieldIndex index = FieldIndex::ForPropertyIndex(*map, i);
+        Object* value = storage->get(i);
+        object->RawFastPropertyAtPut(index, value);
+      }
+    }
+  }
+  object->synchronized_set_map(*map);
 }