cc : Move screen space scale factor to root transform node

cc/trees/property_tree_unittest.cc

Index: cc/trees/property_tree_unittest.cc
diff --git a/cc/trees/property_tree_unittest.cc b/cc/trees/property_tree_unittest.cc
index 3171831efecba42a7420aea352838a36ea8e5b43..5d3e5aa1cff87851f469867f15a9d99c275e5306 100644
--- a/cc/trees/property_tree_unittest.cc
+++ b/cc/trees/property_tree_unittest.cc
@@ -1119,6 +1119,9 @@ class PropertyTreeTestSingularTransformSnapTest : public PropertyTreeTest {
     int parent = tree.Insert(TransformNode(), 0);
     int effect_parent = effect_tree.Insert(EffectNode(), 0);
     effect_tree.Node(effect_parent)->has_render_surface = true;
+    effect_tree.Node(effect_parent)->surface_contents_scale =
+        gfx::Vector2dF(1.f, 1.f);
+
     tree.SetTargetId(parent, parent);
     tree.Node(parent)->scrolls = true;
     tree.Node(parent)->source_node_id = 0;