Generalize scroll parent work in CalculateDrawProperties

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 <list>
 #include <set>
 #include <string>
@@ skipping 251 matching lines @@
 
   ResourceProvider::ResourceId ResourceIdForUIResource(UIResourceId uid) const;
   void ProcessUIResourceRequestQueue();
 
   bool IsUIResourceOpaque(UIResourceId uid) const;
 
   void AddLayerWithCopyOutputRequest(LayerImpl* layer);
   void RemoveLayerWithCopyOutputRequest(LayerImpl* layer);
   const std::vector<LayerImpl*>& LayersWithCopyOutputRequest() const;
 
-  int current_render_surface_list_id() const {
+  size_t current_render_surface_list_id() const {
     return render_surface_layer_list_id_;
   }
 
   LayerImpl* FindFirstScrollingLayerThatIsHitByPoint(
       const gfx::PointF& screen_space_point);
 
   LayerImpl* FindLayerThatIsHitByPoint(const gfx::PointF& screen_space_point);
 
   LayerImpl* FindLayerThatIsHitByPointInTouchHandlerRegion(
       const gfx::PointF& screen_space_point);
@@ skipping 89 matching lines @@
   bool needs_full_tree_sync_;
 
   bool next_activation_forces_redraw_;
 
   bool has_ever_been_drawn_;
 
   ScopedPtrVector<SwapPromise> swap_promise_list_;
 
   UIResourceRequestQueue ui_resource_request_queue_;
 
-  int render_surface_layer_list_id_;
+  size_t render_surface_layer_list_id_;

[danakj, 2014/09/11 19:22:05]

This kinda violates my reading of the chromium style guide. It's a sneaky way of
trying to use unsigned, when this is not in fact the size of a container or
something, where size_t is explicitly allowed.
<quote>
Use an unsigned integer type if your variable represents a bit pattern (e.g. a
hash value or a bitmask).

Use unsigned integer types (preferably size_t) for object and allocation sizes,
object counts, array and pointer offsets, vector indices, and so on.

Do not use unsigned types to mean "this value should never be < 0". For that,
use assertions or run-time checks (as appropriate).
</quote>

It doesn't discuss "if your value can wrap around" but that loosely falls close
to "it can't be < 0", and we should handle wrap around by checking for max() if
it's a problem in practice. Given this hasn't been a problem on the impl side
which generates >= # of frames as the main thread side, I think you should just
leave this as integer and not worry about it?

[Ian Vollick, 2014/09/11 19:58:08]

Done.

 
   // The top controls content offset at the time of the last layout (and thus,
   // viewport resize) in Blink. i.e. How much the viewport was shrunk by the top
   // controls.
   float top_controls_layout_height_;
 
   // The up-to-date content offset of the top controls, i.e. the amount that the
   // web contents have been shifted down from the top of the device viewport.
   float top_controls_top_offset_;
   float top_controls_delta_;
   float sent_top_controls_delta_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(LayerTreeImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_LAYER_TREE_IMPL_H_