cc: Throttle tile priority updates to once a frame.

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 0dff769b565b5453e44e336d719f376dd362bb91..34f06bdb134833765fffafddf57b3faf841eaa33 100644
--- a/cc/layer_tree_impl.cc
+++ b/cc/layer_tree_impl.cc
@@ -121,9 +121,19 @@ void LayerTreeImpl::UpdateMaxScrollOffset() {
   root_scroll_layer_->setMaxScrollOffset(gfx::ToFlooredVector2d(max_scroll));
 }
 
-void LayerTreeImpl::UpdateDrawProperties() {
-  if (!needs_update_draw_properties_)
+struct UpdateTilePrioritiesForLayer {
+  void operator()(LayerImpl *layer) {
+    layer->updateTilePriorities();
+  }
+};
+
+void LayerTreeImpl::UpdateDrawProperties(UpdateDrawPropertiesReason reason) {
+  if (!needs_update_draw_properties_) {
+    if (reason == UPDATE_ACTIVE_TREE_FOR_DRAW && RootLayer())
+      LayerTreeHostCommon::callFunctionForSubtree<UpdateTilePrioritiesForLayer>(

[enne (OOO), 2013/01/25 20:59:10]

I think this might be unneeded.

You should only need to update tile priorities after commit (to initialize) or
when draw properties have changed.  (This patch throttles back how many times we
do it from the second condition.) However, if there's no need to update draw
properties, then there should be equally no need to update tile priorities.

[danakj, 2013/01/25 21:18:15]

The idea is that if you update draw props on scroll (ensureRSLL) but don't
update tile prio at the time, you do it when you draw.

+          RootLayer());
     return;
+  }
 
   needs_update_draw_properties_ = false;
   render_surface_layer_list_.clear();
@@ -144,6 +154,9 @@ void LayerTreeImpl::UpdateDrawProperties() {
 
   {
     TRACE_EVENT1("cc", "LayerTreeImpl::UpdateDrawProperties", "IsActive", IsActiveTree());
+    bool update_tile_priorities =
+        reason == UPDATE_PENDING_TREE ||
+        reason == UPDATE_ACTIVE_TREE_FOR_DRAW;
     LayerTreeHostCommon::calculateDrawProperties(
         RootLayer(),
         device_viewport_size(),
@@ -151,7 +164,8 @@ void LayerTreeImpl::UpdateDrawProperties() {
         pinch_zoom_viewport().page_scale_factor(),
         MaxTextureSize(),
         settings().canUseLCDText,
-        render_surface_layer_list_);
+        render_surface_layer_list_,
+        update_tile_priorities);
   }
 
   DCHECK(!needs_update_draw_properties_) <<