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..c85f19d7248506f110ec8e3482d30da69c06c667 100644
--- a/cc/layers/layer_impl.cc
+++ b/cc/layers/layer_impl.cc
@@ -986,4 +986,22 @@ TransformTree& LayerImpl::GetTransformTree() const {
   return GetPropertyTrees()->transform_tree;
 }
 
+bool LayerImpl::EnsureValidPropertyTreeIndices() const {

[enne (OOO), 2017/06/02 18:41:19]

I know there's a link to the bug at the callsite, but can you add a link to the
bug here too?

[Khushal, 2017/06/02 18:47:02]

Sure. Done.

+  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