Reland use screen space transform to compute translation

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 9bf1ed4430f418fb12d3c74b895135c4575d85ec..cace59787dfc3204b68572de82262e3e1fd2a36c 100644
--- a/cc/trees/property_tree.h
+++ b/cc/trees/property_tree.h
@@ -157,7 +157,9 @@ class CC_EXPORT TransformTree final : public PropertyTree<TransformNode> {
   // Computes the change of basis transform from node |source_id| to |dest_id|.
   // This is used by scroll children to compute transform from their scroll
   // parent space (source) to their parent space (destination) and it can atmost
-  // be a translation.
+  // be a translation. This function assumes that the path from source to
+  // destination has only translations. So, it should not be called when there
+  // can be intermediate 3d transforms but the end result is a translation.
   bool ComputeTranslation(int source_id,
                           int dest_id,
                           gfx::Transform* transform) const;