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

cc/trees/tree_synchronizer.cc

Index: cc/trees/tree_synchronizer.cc
diff --git a/cc/trees/tree_synchronizer.cc b/cc/trees/tree_synchronizer.cc
index 52f1bb384c752137b6ca7f2bfc72139e4bc42ad1..d312d9d2515db04f9ad16897903a57498fe427ec 100644
--- a/cc/trees/tree_synchronizer.cc
+++ b/cc/trees/tree_synchronizer.cc
@@ -74,6 +74,17 @@ std::unique_ptr<LayerImpl> ReuseOrCreateLayerImpl(OwnedLayerImplMap* old_layers,
   return layer_impl;
 }
 
+#if DCHECK_IS_ON()
+template <typename LayerType>
+static bool LayerHasValidPropertyTreeIndices(LayerType* layer) {
+  DCHECK(layer);
+  return layer->transform_tree_index() != TransformTree::kInvalidNodeId &&

[enne (OOO), 2017/04/21 22:57:28]

One thing you might consider is to just make this function void
AssertValidPropertyTreeIndices (with an empty body for !DCHECK_IS_ON, and then
you can assert each of these individually, which might make tracking down a
failure easier.

[jaydasika, 2017/04/25 21:02:38]

Added AssertValidPropertyTreeIndices (we still need
LayerHasValidPropertyTreeIndices also), made sure these functions are only
called when DCHECK_IS_ON = true.

+         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,
@@ -83,6 +94,12 @@ void PushLayerList(OwnedLayerImplMap* old_layers,
     std::unique_ptr<LayerImpl> layer_impl(
         ReuseOrCreateLayerImpl(old_layers, layer, tree_impl));
 
+    // Every layer should have valid property tree indices
+    DCHECK(LayerHasValidPropertyTreeIndices(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));
     tree_impl->AddToLayerList(layer_impl.get());
     tree_impl->AddLayer(std::move(layer_impl));
   }