cc: Fix screen-space transform flattening in CalcDrawProps

cc/trees/layer_tree_host_common.cc

 // Copyright 2011 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/layer_tree_host_common.h"
 
 #include <algorithm>
 
 #include "base/trace_event/trace_event.h"
 #include "cc/base/math_util.h"
@@ skipping 1798 matching lines @@
   layer_draw_properties.target_space_transform = combined_transform;
   // M[draw] = M[parent] * LT * S[layer2content]
   layer_draw_properties.target_space_transform.Scale(
       SK_MScalar1 / layer->contents_scale_x(),
       SK_MScalar1 / layer->contents_scale_y());
 
   // The layer's screen_space_transform represents the transform between root
   // layer's "screen space" and local content space.
   layer_draw_properties.screen_space_transform =
       data_from_ancestor.full_hierarchy_matrix;
-  if (layer->should_flatten_transform())
-    layer_draw_properties.screen_space_transform.FlattenTo2d();
   layer_draw_properties.screen_space_transform.PreconcatTransform
       (layer_draw_properties.target_space_transform);
 
   // Adjusting text AA method during animation may cause repaints, which in-turn
   // causes jank.
   bool adjust_text_aa =
       !animating_opacity_to_screen && !animating_transform_to_screen;
   bool layer_can_use_lcd_text = true;
   bool subtree_can_use_lcd_text = true;
   if (!globals.layers_always_allowed_lcd_text) {
@@ skipping 98 matching lines @@
     layer_draw_properties.target_space_transform_is_animating =
         animating_transform_to_target;
     layer_draw_properties.screen_space_transform_is_animating =
         animating_transform_to_screen;
 
     // Update the aggregate hierarchy matrix to include the transform of the
     // newly created RenderSurfaceImpl.
     data_for_children.full_hierarchy_matrix.PreconcatTransform(
         render_surface->draw_transform());
 
+    // A render surface inherently acts as a flattening point for the content of
+    // its descendants.
+    data_for_children.full_hierarchy_matrix.FlattenTo2d();
+
     if (layer->mask_layer()) {
       DrawProperties<LayerType>& mask_layer_draw_properties =
           layer->mask_layer()->draw_properties();
       mask_layer_draw_properties.render_target = layer;
       mask_layer_draw_properties.visible_content_rect =
           gfx::Rect(layer->content_bounds());
     }
 
     if (layer->replica_layer() && layer->replica_layer()->mask_layer()) {
       DrawProperties<LayerType>& replica_mask_draw_properties =
@@ skipping 648 matching lines @@
       inputs->current_render_surface_layer_list_id);
 
   // The dummy layer list should not have been used.
   DCHECK_EQ(0u, dummy_layer_list.size());
   // A root layer render_surface should always exist after
   // CalculateDrawProperties.
   DCHECK(inputs->root_layer->render_surface());
 }
 
 }  // namespace cc