cc: Make impl-thread property trees handle fixed-position layers

cc/layers/layer_position_constraint_unittest.cc

Index: cc/layers/layer_position_constraint_unittest.cc
diff --git a/cc/layers/layer_position_constraint_unittest.cc b/cc/layers/layer_position_constraint_unittest.cc
index 68a208915e1dd8198ce5b5b9561ec8f7ee6bbdc2..19b6803d7c412614f463ab309af3f6eb4eef5111 100644
--- a/cc/layers/layer_position_constraint_unittest.cc
+++ b/cc/layers/layer_position_constraint_unittest.cc
@@ -975,6 +975,7 @@ TEST_F(LayerPositionConstraintTest,
   child_->SetIsContainerForFixedPositionLayers(true);
   grand_child_->SetPositionConstraint(fixed_to_top_left_);
   great_grand_child_->SetIsContainerForFixedPositionLayers(true);
+  great_grand_child_->SetScrollClipLayerId(root_->id());

[ajuma, 2015/05/29 17:47:08]

This test scrolls great_grand_child_, so it should be scrollable (so that a
transform node gets created).

[enne (OOO), 2015/05/29 20:07:53]

Is that something that can be DCHECK'd?

[ajuma, 2015/05/29 21:41:07]

Added a DCHECK to LayerImpl::SetScrollDelta.

   great_great_grand_child->SetPositionConstraint(fixed_to_top_left_);
 
   CommitAndUpdateImplPointers();