cc : Add DCHECKs to ensure we have valid proprety tree indices at commit

cc/trees/tree_synchronizer.cc

 // Copyright 2011 The Chromium 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 "cc/trees/tree_synchronizer.h"
 
 #include <stddef.h>
 
 #include <set>
 
@@ skipping 56 matching lines @@
                                                   LayerType* layer,
                                                   LayerTreeImpl* tree_impl) {
   if (!layer)
     return nullptr;
   std::unique_ptr<LayerImpl> layer_impl = std::move((*old_layers)[layer->id()]);
   if (!layer_impl)
     layer_impl = layer->CreateLayerImpl(tree_impl);
   return layer_impl;
 }
 
+#if DCHECK_IS_ON()
+template <typename LayerType>
+static void AssertValidPropertyTreeIndices(LayerType* layer) {
+  DCHECK(layer);
+  DCHECK_NE(layer->transform_tree_index(), TransformTree::kInvalidNodeId);
+  DCHECK_NE(layer->effect_tree_index(), EffectTree::kInvalidNodeId);
+  DCHECK_NE(layer->clip_tree_index(), ClipTree::kInvalidNodeId);
+  DCHECK_NE(layer->scroll_tree_index(), ScrollTree::kInvalidNodeId);
+}
+
+static bool LayerHasValidPropertyTreeIndices(LayerImpl* layer) {
+  DCHECK(layer);
+  return layer->transform_tree_index() != TransformTree::kInvalidNodeId &&
+         layer->effect_tree_index() != EffectTree::kInvalidNodeId &&
+         layer->clip_tree_index() != ClipTree::kInvalidNodeId &&
+         layer->scroll_tree_index() != ScrollTree::kInvalidNodeId;
+}
+#endif
+
 template <typename LayerTreeType>
 void PushLayerList(OwnedLayerImplMap* old_layers,
                    LayerTreeType* host,
                    LayerTreeImpl* tree_impl) {
   tree_impl->ClearLayerList();
   for (auto* layer : *host) {
     std::unique_ptr<LayerImpl> layer_impl(
         ReuseOrCreateLayerImpl(old_layers, layer, tree_impl));
 
+#if DCHECK_IS_ON()
+    // Every layer should have valid property tree indices
+    AssertValidPropertyTreeIndices(layer);
+    // Every layer_impl should either have valid property tree indices already
+    // or the corresponding layer should push them onto layer_impl.
+    DCHECK(LayerHasValidPropertyTreeIndices(layer_impl.get()) ||
+           host->LayerNeedsPushPropertiesForTesting(layer));
+#endif
+
     tree_impl->AddToLayerList(layer_impl.get());
     tree_impl->AddLayer(std::move(layer_impl));
   }
   tree_impl->OnCanDrawStateChangedForTree();
 }
 
 template <typename LayerType>
 static void PushLayerPropertiesInternal(
     std::unordered_set<LayerType*> layers_that_should_push_properties,
     LayerTreeImpl* impl_tree) {
@@ skipping 10 matching lines @@
                               active_tree);
 }
 
 void TreeSynchronizer::PushLayerProperties(LayerTreeHost* host_tree,
                                            LayerTreeImpl* impl_tree) {
   PushLayerPropertiesInternal(host_tree->LayersThatShouldPushProperties(),
                               impl_tree);
 }
 
 }  // namespace cc