Add more out of line copy ctors for complex classes.

cc/trees/property_tree.h

Index: cc/trees/property_tree.h
diff --git a/cc/trees/property_tree.h b/cc/trees/property_tree.h
index 9115702aa039f78a50c0cc9e0b8c63ba28d1a7cb..4c1fab2ebfd43a43d6934a04f6eeb85d15102b32 100644
--- a/cc/trees/property_tree.h
+++ b/cc/trees/property_tree.h
@@ -556,6 +556,7 @@ class CC_EXPORT EffectTree final : public PropertyTree<EffectNode> {
 class CC_EXPORT ScrollTree final : public PropertyTree<ScrollNode> {
  public:
   ScrollTree();
+  ScrollTree(const ScrollTree& other);
   ~ScrollTree() override;
 
   ScrollTree& operator=(const ScrollTree& from);
@@ -619,6 +620,7 @@ class CC_EXPORT ScrollTree final : public PropertyTree<ScrollNode> {
 class CC_EXPORT PropertyTrees final {
  public:
   PropertyTrees();
+  PropertyTrees(const PropertyTrees& other);
   ~PropertyTrees();
 
   bool operator==(const PropertyTrees& other) const;