Add a sanity check to ensure that CDP doesn't hit a cycle

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 "cc/trees/occlusion.h"
 #include "third_party/skia/include/core/SkXfermode.h"
@@ skipping 16 matching lines @@
         can_use_lcd_text(false),
         is_clipped(false),
         render_target(nullptr),
         contents_scale_x(1.f),
         contents_scale_y(1.f),
         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),
+        visited(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),
         ideal_contents_scale(0.f),
         maximum_animation_contents_scale(0.f),
         page_scale_factor(0.f),
         device_scale_factor(0.f) {}
 
@@ skipping 69 matching lines @@
   // This is true if the layer has any direct child that has a scroll parent.
   // This layer will not be the scroll parent in this case. This information
   // lets us avoid work in CalculateDrawPropertiesInternal -- if none of our
   // children have scroll parents, we will not need to recur out of order.
   bool has_child_with_a_scroll_parent;
 
   // This is true if the order (wrt to its siblings in the tree) in which the
   // layer will be visited while computing draw properties has been determined.
   bool sorted_for_recursion;
 
+  // This is used to sanity-check CDP and ensure that we don't revisit a layer.
+  bool visited;
+
   // If this layer is visited out of order, its contribution to the descendant
   // and render surface layer lists will be put aside in a temporary list.
   // These values will allow for an efficient reordering of these additions.
   size_t index_of_first_descendants_addition;
   size_t num_descendants_added;
   size_t index_of_first_render_surface_layer_list_addition;
   size_t num_render_surfaces_added;
 
   // Each time we generate a new render surface layer list, an ID is used to
   // identify it. |last_drawn_render_surface_layer_list_id| is set to the ID
@@ skipping 16 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_