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

cc/trees/property_tree_builder.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/trees/property_tree_builder.h"
 
 #include <map>
 #include <set>
 
 #include "cc/base/math_util.h"
@@ skipping 194 matching lines @@
         source_offset = data_from_ancestor.transform_tree_parent
                             ->offset_to_transform_parent();
         source_index =
             data_from_ancestor.transform_tree_parent->transform_tree_index();
       }
       source_offset += data_from_ancestor.scroll_compensation_adjustment;
     }
   }
 
   if (layer->IsContainerForFixedPositionLayers() || is_root) {
-    DCHECK(!is_scrollable || layer->transform().IsIdentity());
-    data_for_children->transform_fixed_parent = layer;
+    if (is_scrollable) {
+      DCHECK(!is_root);
+      DCHECK(layer->transform().IsIdentity());
+      data_for_children->transform_fixed_parent = layer->parent();
+    } else {
+      data_for_children->transform_fixed_parent = layer;
+    }
   }
   data_for_children->transform_tree_parent = layer;
 
   if (layer->IsContainerForFixedPositionLayers() || is_fixed)
     data_for_children->scroll_compensation_adjustment = gfx::Vector2dF();
 
   if (!requires_node) {
     data_for_children->should_flatten |= layer->should_flatten_transform();
     gfx::Vector2dF local_offset = layer->position().OffsetFromOrigin() +
                                   layer->transform().To2dTranslation();
@@ skipping 152 matching lines @@
 }  // namespace
 
 template <typename LayerType>
 void BuildPropertyTreesTopLevelInternal(LayerType* root_layer,
                                         const LayerType* page_scale_layer,
                                         float page_scale_factor,
                                         float device_scale_factor,
                                         const gfx::Rect& viewport,
                                         const gfx::Transform& device_transform,
                                         PropertyTrees* property_trees) {
+  if (!property_trees->needs_rebuild)
+    return;
+
   property_trees->sequence_number++;
 
   DataForRecursion<LayerType> data_for_recursion;
   data_for_recursion.transform_tree = &property_trees->transform_tree;
   data_for_recursion.clip_tree = &property_trees->clip_tree;
   data_for_recursion.opacity_tree = &property_trees->opacity_tree;
   data_for_recursion.transform_tree_parent = nullptr;
   data_for_recursion.transform_fixed_parent = nullptr;
   data_for_recursion.render_target = root_layer;
   data_for_recursion.clip_tree_parent = 0;
@@ skipping 27 matching lines @@
 }
 
 void PropertyTreeBuilder::BuildPropertyTrees(
     Layer* root_layer,
     const Layer* page_scale_layer,
     float page_scale_factor,
     float device_scale_factor,
     const gfx::Rect& viewport,
     const gfx::Transform& device_transform,
     PropertyTrees* property_trees) {
-  // TODO(enne): hoist this out of here
-  if (!property_trees->needs_rebuild)
-    return;
-
   BuildPropertyTreesTopLevelInternal(
       root_layer, page_scale_layer, page_scale_factor, device_scale_factor,
       viewport, device_transform, property_trees);
 }
 
 void PropertyTreeBuilder::BuildPropertyTrees(
     LayerImpl* root_layer,
     const LayerImpl* page_scale_layer,
     float page_scale_factor,
     float device_scale_factor,
     const gfx::Rect& viewport,
     const gfx::Transform& device_transform,
     PropertyTrees* property_trees) {
   BuildPropertyTreesTopLevelInternal(
       root_layer, page_scale_layer, page_scale_factor, device_scale_factor,
       viewport, device_transform, property_trees);
 }
 
 }  // namespace cc