Keeping track of descendants that draw content instead of recalcualting

cc/layers/draw_properties.h

 // Copyright 2012 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.
 
 #ifndef CC_LAYERS_DRAW_PROPERTIES_H_
 #define CC_LAYERS_DRAW_PROPERTIES_H_
 
 #include "base/memory/scoped_ptr.h"
 #include "ui/gfx/rect.h"
 #include "ui/gfx/transform.h"
 
 namespace cc {
 
 // Container for properties that layers need to compute before they can be
 // drawn.
 template <typename LayerType>
 struct CC_EXPORT DrawProperties {
   DrawProperties()
       : opacity(0.f),
         opacity_is_animating(false),
         screen_space_opacity_is_animating(false),
         target_space_transform_is_animating(false),
         screen_space_transform_is_animating(false),
         can_use_lcd_text(false),
         is_clipped(false),
         render_target(NULL),
         contents_scale_x(1.f),
         contents_scale_y(1.f),
-        num_descendants_that_draw_content(0),
         num_unclipped_descendants(0),
         layer_or_descendant_has_copy_request(false),
         layer_or_descendant_has_input_handler(false),
         has_child_with_a_scroll_parent(false),
         sorted_for_recursion(false),
         index_of_first_descendants_addition(0),
         num_descendants_added(0),
         index_of_first_render_surface_layer_list_addition(0),
         num_render_surfaces_added(0),
         last_drawn_render_surface_layer_list_id(0),
@@ skipping 49 matching lines @@
   gfx::Rect clip_rect;
 
   // The scale used to move between layer space and content space, and bounds
   // of the space. One is always a function of the other, but which one
   // depends on the layer type. For picture layers, this is an ideal scale,
   // and not always the one used.
   float contents_scale_x;
   float contents_scale_y;
   gfx::Size content_bounds;
 
-  // Does not include this layer itself, only its children and descendants.
-  int num_descendants_that_draw_content;
-
   // Number of descendants with a clip parent that is our ancestor. NB - this
   // does not include our clip children because they are clipped by us.
   int num_unclipped_descendants;
 
   // If true, the layer or some layer in its sub-tree has a CopyOutputRequest
   // present on it.
   bool layer_or_descendant_has_copy_request;
 
   // If true, the layer or one of its descendants has a wheel or touch handler.
   bool layer_or_descendant_has_input_handler;
@@ skipping 37 matching lines @@
   // have page scale applied and others not, this may differ between layers.
   float page_scale_factor;
 
   // The device scale factor that is applied to the layer.
   float device_scale_factor;
 };
 
 }  // namespace cc
 
 #endif  // CC_LAYERS_DRAW_PROPERTIES_H_