cc : Move screen space scale factor to root transform node

cc/trees/property_tree_builder.cc

Index: cc/trees/property_tree_builder.cc
diff --git a/cc/trees/property_tree_builder.cc b/cc/trees/property_tree_builder.cc
index 2ad73f16529b919037f8de37bb3761280031b17b..8d3f4ef189d58e50bcfa112fa2dfc9b1950eda07 100644
--- a/cc/trees/property_tree_builder.cc
+++ b/cc/trees/property_tree_builder.cc
@@ -630,12 +630,10 @@ bool AddTransformNodeIfNeeded(
   }
 
   float post_local_scale_factor = 1.0f;
-  if (is_root)
-    post_local_scale_factor =
-        data_for_children->property_trees->transform_tree.device_scale_factor();
 
   if (is_page_scale_layer) {
-    post_local_scale_factor *= data_from_ancestor.page_scale_factor;
+    if (!is_root)
+      post_local_scale_factor *= data_from_ancestor.page_scale_factor;
     data_for_children->property_trees->transform_tree.set_page_scale_factor(
         data_from_ancestor.page_scale_factor);
   }
@@ -646,10 +644,14 @@ bool AddTransformNodeIfNeeded(
   node->source_node_id = source_index;
   node->post_local_scale_factor = post_local_scale_factor;
   if (is_root) {
-    data_for_children->property_trees->transform_tree.SetDeviceTransform(
-        *data_from_ancestor.device_transform, layer->position());
+    float page_scale_factor_for_root =
+        is_page_scale_layer ? data_from_ancestor.page_scale_factor : 1.f;
     data_for_children->property_trees->transform_tree
-        .SetDeviceTransformScaleFactor(*data_from_ancestor.device_transform);
+        .SetRootTransformsAndScales(data_for_children->property_trees
+                                        ->transform_tree.device_scale_factor(),
+                                    page_scale_factor_for_root,
+                                    *data_from_ancestor.device_transform,
+                                    layer->position());
   } else {
     node->source_offset = source_offset;
     node->update_post_local_transform(layer->position(),
@@ -1346,8 +1348,11 @@ void BuildPropertyTreesTopLevelInternal(
     draw_property_utils::UpdateElasticOverscroll(
         property_trees, overscroll_elasticity_layer, elastic_overscroll);
     property_trees->clip_tree.SetViewportClip(gfx::RectF(viewport));
-    property_trees->transform_tree.SetDeviceTransform(device_transform,
-                                                      root_layer->position());
+    float page_scale_factor_for_root =
+        page_scale_layer == root_layer ? page_scale_factor : 1.f;
+    property_trees->transform_tree.SetRootTransformsAndScales(
+        device_scale_factor, page_scale_factor_for_root, device_transform,
+        root_layer->position());
     return;
   }
 
@@ -1391,6 +1396,7 @@ void BuildPropertyTreesTopLevelInternal(
   root_clip.applies_local_clip = true;
   root_clip.clip = gfx::RectF(viewport);
   root_clip.transform_id = kRootPropertyTreeNodeId;
+  root_clip.target_transform_id = kRootPropertyTreeNodeId;
   data_for_recursion.clip_tree_parent =
       data_for_recursion.property_trees->clip_tree.Insert(
           root_clip, kRootPropertyTreeNodeId);