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

cc/trees/layer_tree_impl.cc

Index: cc/trees/layer_tree_impl.cc
diff --git a/cc/trees/layer_tree_impl.cc b/cc/trees/layer_tree_impl.cc
index eadc4043ab43621b06a0cc02fd7f4d000651856b..03a100e5ea1c7faed41f947b37f86d112c34e585 100644
--- a/cc/trees/layer_tree_impl.cc
+++ b/cc/trees/layer_tree_impl.cc
@@ -252,13 +252,7 @@ void LayerTreeImpl::UpdateSolidColorScrollbars() {
   }
 }
 
-struct UpdateTilePrioritiesForLayer {
-  void operator()(LayerImpl *layer) {
-    layer->UpdateTilePriorities();
-  }
-};
-
-void LayerTreeImpl::UpdateDrawProperties(UpdateDrawPropertiesReason reason) {
+void LayerTreeImpl::UpdateDrawProperties() {
   if (IsActiveTree() && RootScrollLayer() && RootClipLayer())
     UpdateRootScrollLayerSizeDelta();
 
@@ -275,13 +269,6 @@ void LayerTreeImpl::UpdateDrawProperties(UpdateDrawPropertiesReason reason) {
       RootClipLayer()->SetMasksToBounds(false);
   }
 
-  if (!needs_update_draw_properties_) {
-    if (reason == UPDATE_ACTIVE_TREE_FOR_DRAW && root_layer())
-      LayerTreeHostCommon::CallFunctionForSubtree<UpdateTilePrioritiesForLayer>(
-          root_layer());
-    return;
-  }
-
   needs_update_draw_properties_ = false;
   render_surface_layer_list_.clear();
 
@@ -303,9 +290,12 @@ void LayerTreeImpl::UpdateDrawProperties(UpdateDrawPropertiesReason reason) {
                  "LayerTreeImpl::UpdateDrawProperties",
                  "IsActive",
                  IsActiveTree());
+
+    base::TimeTicks frame_time = CurrentFrameTime();
     bool update_tile_priorities =
-        reason == UPDATE_PENDING_TREE ||
-        reason == UPDATE_ACTIVE_TREE_FOR_DRAW;
+        frame_time != frame_time_last_update_tile_priorities_;
+    frame_time_last_update_tile_priorities_ = frame_time;
+
     LayerTreeHostCommon::CalculateDrawProperties(
         root_layer(),
         device_viewport_size(),
@@ -318,7 +308,7 @@ void LayerTreeImpl::UpdateDrawProperties(UpdateDrawPropertiesReason reason) {
   }
 
   DCHECK(!needs_update_draw_properties_) <<
-      "calcDrawProperties should not set_needs_update_draw_properties()";
+      "CalcDrawProperties should not set_needs_update_draw_properties()";
 }
 
 static void ClearRenderSurfacesOnLayerImplRecursive(LayerImpl* current) {
@@ -382,6 +372,9 @@ void LayerTreeImpl::PushPersistedState(LayerTreeImpl* pending_tree) {
   int id = currently_scrolling_layer_ ? currently_scrolling_layer_->id() : 0;
   pending_tree->SetCurrentlyScrollingLayer(
       LayerTreeHostCommon::FindLayerInSubtree(pending_tree->root_layer(), id));
+
+  frame_time_last_update_tile_priorities_ =
+      pending_tree->frame_time_last_update_tile_priorities_;
 }
 
 static void DidBecomeActiveRecursive(LayerImpl* layer) {