cc: Make UpdateTilePriorities a separate step

This will make it more obvious in traces where work is really being done
and make it possible to optimize this further.

Comparing average times spent in the renderer compositor while scrolling
Wikipedia's List of Pokemon page on an N4 in two different runs:

    Before change:
        UpdateDrawProperties: 0.754ms

    After change:
        UpdateDrawProperties: 0.249ms
        UpdateTilePriorities: 0.553ms

R=danakj@chromium.org
BUG=308244

Review URL: https://codereview.chromium.org/26880009

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@229590 0039d316-1c4b-4281-b951-d872f2087c98

2 files changed, 31 insertions, 17 deletions

diff --git a/cc/trees/layer_tree_host_common.cc b/cc/trees/layer_tree_host_common.cc
index c9d453f..8bab4ab 100644
--- a/cc/trees/layer_tree_host_common.cc
+++ b/cc/trees/layer_tree_host_common.cc
@@ -525,22 +525,6 @@ static inline bool SubtreeShouldBeSkipped(Layer* layer,
          !layer->OpacityCanAnimateOnImplThread();
 }
 
-// Called on each layer that could be drawn after all information from
-// CalcDrawProperties has been updated on that layer.  May have some false
-// positives (e.g. layers get this called on them but don't actually get drawn).
-static inline void UpdateTilePrioritiesForLayer(LayerImpl* layer) {
-  layer->UpdateTilePriorities();
-
-  // Mask layers don't get this call, so explicitly update them so they can
-  // kick off tile rasterization.
-  if (layer->mask_layer())
-    layer->mask_layer()->UpdateTilePriorities();
-  if (layer->replica_layer() && layer->replica_layer()->mask_layer())
-    layer->replica_layer()->mask_layer()->UpdateTilePriorities();
-}
-
-static inline void UpdateTilePrioritiesForLayer(Layer* layer) {}
-
 static inline void SavePaintPropertiesLayer(LayerImpl* layer) {}
 
 static inline void SavePaintPropertiesLayer(Layer* layer) {
@@ -2092,7 +2076,6 @@ static void CalculateDrawPropertiesInternal(
     }
   }
 
-  UpdateTilePrioritiesForLayer(layer);
   SavePaintPropertiesLayer(layer);
 
   // If neither this layer nor any of its children were added, early out.
diff --git a/cc/trees/layer_tree_impl.cc b/cc/trees/layer_tree_impl.cc
index 471a133..d124a63 100644
--- a/cc/trees/layer_tree_impl.cc
+++ b/cc/trees/layer_tree_impl.cc
@@ -385,6 +385,37 @@ void LayerTreeImpl::UpdateDrawProperties() {
     LayerTreeHostCommon::CalculateDrawProperties(&inputs);
   }
 
+  {
+    TRACE_EVENT2("cc",
+                 "LayerTreeImpl::UpdateTilePriorities",
+                 "IsActive",
+                 IsActiveTree(),
+                 "SourceFrameNumber",
+                 source_frame_number_);
+    // LayerIterator is used here instead of CallFunctionForSubtree to only
+    // UpdateTilePriorities on layers that will be visible (and thus have valid
+    // draw properties) and not because any ordering is required.
+    typedef LayerIterator<LayerImpl,
+                          LayerImplList,
+                          RenderSurfaceImpl,
+                          LayerIteratorActions::FrontToBack> LayerIteratorType;
+    LayerIteratorType end = LayerIteratorType::End(&render_surface_layer_list_);
+    for (LayerIteratorType it =
+             LayerIteratorType::Begin(&render_surface_layer_list_);
+         it != end;
+         ++it) {
+      if (!it.represents_itself())
+        continue;
+      LayerImpl* layer = *it;
+
+      layer->UpdateTilePriorities();
+      if (layer->mask_layer())
+        layer->mask_layer()->UpdateTilePriorities();
+      if (layer->replica_layer() && layer->replica_layer()->mask_layer())
+        layer->replica_layer()->mask_layer()->UpdateTilePriorities();
+    }
+  }
+
   DCHECK(!needs_update_draw_properties_) <<
       "CalcDrawProperties should not set_needs_update_draw_properties()";
 }