Reland of cc : Make LayerImpl destruction independent of tree hierarchy

cc/layers/layer_impl.h

 // 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.
 
 #ifndef CC_LAYERS_LAYER_IMPL_H_
 #define CC_LAYERS_LAYER_IMPL_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 142 matching lines @@
   bool has_render_surface() const { return !!render_surface(); }
 
   void SetMaskLayer(std::unique_ptr<LayerImpl> mask_layer);
   LayerImpl* mask_layer() { return mask_layer_; }
   const LayerImpl* mask_layer() const { return mask_layer_; }
   std::unique_ptr<LayerImpl> TakeMaskLayer();
 
   void SetReplicaLayer(std::unique_ptr<LayerImpl> replica_layer);
   LayerImpl* replica_layer() { return replica_layer_; }
   const LayerImpl* replica_layer() const { return replica_layer_; }
-  std::unique_ptr<LayerImpl> TakeReplicaLayer();
+  std::unique_ptr<LayerImpl> TakeReplicaLayerForTesting();
 
   bool has_mask() const { return !!mask_layer_; }
   bool has_replica() const { return !!replica_layer_; }
   bool replica_has_mask() const {
     return replica_layer_ && (mask_layer_ || replica_layer_->mask_layer_);
   }
 
   LayerTreeImpl* layer_tree_impl() const { return layer_tree_impl_; }
 
   void PopulateSharedQuadState(SharedQuadState* state) const;
@@ skipping 354 matching lines @@
   void AppendDebugBorderQuad(RenderPass* render_pass,
                              const gfx::Size& bounds,
                              const SharedQuadState* shared_quad_state,
                              AppendQuadsData* append_quads_data,
                              SkColor color,
                              float width) const;
 
   gfx::Rect GetScaledEnclosingRectInTargetSpace(float scale) const;
 
  private:
-  // Warning: This does not preserve tree structure invariants.
-  void ClearChildList();
-
   void ValidateQuadResourcesInternal(DrawQuad* quad) const;
 
   virtual const char* LayerTypeAsString() const;
 
   // Properties internal to LayerImpl
   LayerImpl* parent_;
   LayerImplList children_;
 
   // mask_layer_ can be temporarily stolen during tree sync, we need this ID to
   // confirm newly assigned layer is still the previous one
@@ skipping 91 matching lines @@
 
   bool scrolls_drawn_descendant_;
   bool has_will_change_transform_hint_;
 
   DISALLOW_COPY_AND_ASSIGN(LayerImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_LAYERS_LAYER_IMPL_H_