cc: Simplify the logic for deciding to update tile priorities.

cc/layer_tree_impl.cc

Index: cc/layer_tree_impl.cc
diff --git a/cc/layer_tree_impl.cc b/cc/layer_tree_impl.cc
index b0d071efd64d7bf84ccca61ad9c15dd0fc246474..c3cb7089b3046d9a90814bf695a5d9dbd15dd423 100644
--- a/cc/layer_tree_impl.cc
+++ b/cc/layer_tree_impl.cc
@@ -29,6 +29,7 @@ LayerTreeImpl::LayerTreeImpl(LayerTreeHostImpl* layer_tree_host_impl)
       contents_textures_purged_(false),
       viewport_size_invalid_(false),
       needs_update_draw_properties_(true),
+      needs_update_tile_priorities_(false),
       needs_full_tree_sync_(true) {
 }
 
@@ -219,13 +220,17 @@ struct UpdateTilePrioritiesForLayer {
 
 void LayerTreeImpl::UpdateDrawProperties(UpdateDrawPropertiesReason reason) {
   if (!needs_update_draw_properties_) {
-    if (reason == UPDATE_ACTIVE_TREE_FOR_DRAW && RootLayer())
+    if (needs_update_tile_priorities_ && RootLayer()) {
+      DCHECK_EQ(UPDATE_ACTIVE_TREE_FOR_DRAW, reason);

[enne (OOO), 2013/03/04 20:16:39]

The change that added this UpdateDrawProperties reason had good performance
benefits, but I still feel like it's a lot of complexity to keep in your head
about at what point what gets updated and why.

Given that this patch provides needs_update_tile_priorities, can you get rid of
UpdateDrawPropertiesReason using the new flag instead? For instance, it's a
little weird that you have needs_update_tile_priorities, but
update_tile_priorities isn't always equal to it.

       LayerTreeHostCommon::callFunctionForSubtree<UpdateTilePrioritiesForLayer>(
           RootLayer());
+      needs_update_tile_priorities_ = false;
+    }
     return;
   }
 
   needs_update_draw_properties_ = false;
+  needs_update_tile_priorities_ = true;
   render_surface_layer_list_.clear();
 
   // For maxTextureSize.
@@ -255,6 +260,9 @@ void LayerTreeImpl::UpdateDrawProperties(UpdateDrawPropertiesReason reason) {
         settings().canUseLCDText,
         render_surface_layer_list_,
         update_tile_priorities);
+
+    if (update_tile_priorities)
+      needs_update_tile_priorities_ = false;
   }
 
   DCHECK(!needs_update_draw_properties_) <<