Refactor SetViewportLayerIds to use a struct instead of 6 values

cc/trees/layer_tree_impl.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_TREES_LAYER_TREE_IMPL_H_
 #define CC_TREES_LAYER_TREE_IMPL_H_
 
 #include <map>
 #include <set>
 #include <string>
@@ skipping 184 matching lines @@
   void set_is_first_frame_after_commit(bool is_first_frame_after_commit) {
     is_first_frame_after_commit_tracker_ =
         is_first_frame_after_commit ? -1 : source_frame_number_;
   }
 
   HeadsUpDisplayLayerImpl* hud_layer() { return hud_layer_; }
   void set_hud_layer(HeadsUpDisplayLayerImpl* layer_impl) {
     hud_layer_ = layer_impl;
   }
 
-  LayerImpl* InnerViewportScrollLayer() const;
-  // This function may return NULL, it is the caller's responsibility to check.
-  LayerImpl* OuterViewportScrollLayer() const;
   gfx::ScrollOffset TotalScrollOffset() const;
   gfx::ScrollOffset TotalMaxScrollOffset() const;
 
-  LayerImpl* InnerViewportContainerLayer() const;
-  LayerImpl* OuterViewportContainerLayer() const;
   ScrollNode* CurrentlyScrollingNode();
   const ScrollNode* CurrentlyScrollingNode() const;
   int LastScrolledScrollNodeIndex() const;
   void SetCurrentlyScrollingNode(ScrollNode* node);
   void ClearCurrentlyScrollingNode();
 
-  void SetViewportLayersFromIds(int overscroll_elasticity_layer,
-                                int page_scale_layer_id,
-                                int inner_viewport_container_layer_id,
-                                int outer_viewport_container_layer_id,
-                                int inner_viewport_scroll_layer_id,
-                                int outer_viewport_scroll_layer_id);
+  struct ViewportLayerIds {
+    int overscroll_elasticity = Layer::INVALID_ID;
+    int page_scale = Layer::INVALID_ID;
+    int inner_viewport_container = Layer::INVALID_ID;
+    int outer_viewport_container = Layer::INVALID_ID;
+    int inner_viewport_scroll = Layer::INVALID_ID;
+    int outer_viewport_scroll = Layer::INVALID_ID;
+  };
+  void SetViewportLayersFromIds(const ViewportLayerIds& viewport_layer_ids);
   void ClearViewportLayers();
-  LayerImpl* OverscrollElasticityLayer() {
-    return LayerById(overscroll_elasticity_layer_id_);
+  LayerImpl* OverscrollElasticityLayer() const {
+    return LayerById(viewport_layer_ids_.overscroll_elasticity);
   }
-  LayerImpl* PageScaleLayer() { return LayerById(page_scale_layer_id_); }
+  LayerImpl* PageScaleLayer() const {
+    return LayerById(viewport_layer_ids_.page_scale);
+  }
+  LayerImpl* InnerViewportContainerLayer() const {
+    return LayerById(viewport_layer_ids_.inner_viewport_container);
+  }
+  LayerImpl* OuterViewportContainerLayer() const {
+    return LayerById(viewport_layer_ids_.outer_viewport_container);
+  }
+  LayerImpl* InnerViewportScrollLayer() const {
+    return LayerById(viewport_layer_ids_.inner_viewport_scroll);
+  }
+  LayerImpl* OuterViewportScrollLayer() const {
+    return LayerById(viewport_layer_ids_.outer_viewport_scroll);
+  }
+
   void ApplySentScrollAndScaleDeltasFromAbortedCommit();
 
   SkColor background_color() const { return background_color_; }
   void set_background_color(SkColor color) { background_color_ = color; }
 
   bool has_transparent_background() const {
     return has_transparent_background_;
   }
   void set_has_transparent_background(bool transparent) {
     has_transparent_background_ = transparent;
@@ skipping 280 matching lines @@
   LayerTreeHostImpl* layer_tree_host_impl_;
   int source_frame_number_;
   int is_first_frame_after_commit_tracker_;
   LayerImpl* root_layer_for_testing_;
   HeadsUpDisplayLayerImpl* hud_layer_;
   PropertyTrees property_trees_;
   SkColor background_color_;
   bool has_transparent_background_;
 
   int last_scrolled_scroll_node_index_;
-  int overscroll_elasticity_layer_id_;
-  int page_scale_layer_id_;
 
-  int inner_viewport_container_layer_id_;
-  int outer_viewport_container_layer_id_;
-
-  int inner_viewport_scroll_layer_id_;
-  int outer_viewport_scroll_layer_id_;
+  ViewportLayerIds viewport_layer_ids_;
 
   LayerSelection selection_;
 
   scoped_refptr<SyncedProperty<ScaleGroup>> page_scale_factor_;
   float min_page_scale_factor_;
   float max_page_scale_factor_;
 
   float device_scale_factor_;
   float painted_device_scale_factor_;
   gfx::ColorSpace raster_color_space_;
@@ skipping 78 matching lines @@
   // lifecycle states. See: |LayerTreeLifecycle|.
   LayerTreeLifecycle lifecycle_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(LayerTreeImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_LAYER_TREE_IMPL_H_