cc: Workaround invalid property tree state on Layers.

cc/layers/layer_impl.cc

Index: cc/layers/layer_impl.cc
diff --git a/cc/layers/layer_impl.cc b/cc/layers/layer_impl.cc
index 57cb1b4a3de5abed980fd9765511fee56adb1381..1820e1b56410c7c1c904c3b88dd8f42a9780af04 100644
--- a/cc/layers/layer_impl.cc
+++ b/cc/layers/layer_impl.cc
@@ -986,4 +986,26 @@ TransformTree& LayerImpl::GetTransformTree() const {
   return GetPropertyTrees()->transform_tree;
 }
 
+bool LayerImpl::HasValidPropertyTreeIndices() const {
+  // TODO(crbug.com/726423): LayerImpls should never have invalid PropertyTree
+  // indices.
+  const bool has_valid_transform_node =
+      !!GetTransformTree().Node(transform_tree_index());
+  DCHECK(has_valid_transform_node);
+
+  const bool has_valid_effect_node =
+      !!GetEffectTree().Node(effect_tree_index());
+  DCHECK(has_valid_effect_node);
+
+  const bool has_valid_clip_node = !!GetClipTree().Node(clip_tree_index());
+  DCHECK(has_valid_clip_node);
+
+  const bool has_valid_scroll_node =
+      !!GetScrollTree().Node(scroll_tree_index());
+  DCHECK(has_valid_scroll_node);
+
+  return has_valid_transform_node && has_valid_effect_node &&
+         has_valid_clip_node && has_valid_scroll_node;
+}
+
 }  // namespace cc