Generalize scroll parent work in CalculateDrawProperties

cc/trees/layer_tree_impl.h

Index: cc/trees/layer_tree_impl.h
diff --git a/cc/trees/layer_tree_impl.h b/cc/trees/layer_tree_impl.h
index efe778f6830f5b8b69145fbf4f0d4e3fb1b5e525..367fc716df1f150ba40dd958e7c18b750aa6282e 100644
--- a/cc/trees/layer_tree_impl.h
+++ b/cc/trees/layer_tree_impl.h
@@ -269,7 +269,7 @@ class CC_EXPORT LayerTreeImpl {
   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_;
   }
 
@@ -379,7 +379,7 @@ class CC_EXPORT LayerTreeImpl {
 
   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