cc: Ensure that layers with invalid tile priorities don't raster.

This patch ensures that when a layer is does not have valid tile
priorities (ie it's recycled, or it's not in the render surface
layer list), then the raster iterator will not return any tiles.

BUG=381704
R=reveman

Review URL: https://codereview.chromium.org/329383002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@276896 0039d316-1c4b-4281-b951-d872f2087c98

cc/layers/picture_layer_impl.cc

@@ -1442,11 +1442,20 @@ PictureLayerImpl::LayerRasterTileIterator::LayerRasterTileIterator(
     bool prioritize_low_res)
     : layer_(layer), current_stage_(0) {
   DCHECK(layer_);
+
+  // Early out if the layer has no tilings.
   if (!layer_->tilings_ || !layer_->tilings_->num_tilings()) {
     current_stage_ = arraysize(stages_);
     return;
   }
 
+  // Tiles without valid priority are treated as having lowest priority and
+  // never considered for raster.
+  if (!layer_->HasValidTilePriorities()) {
+    current_stage_ = arraysize(stages_);
+    return;
+  }
+
   WhichTree tree =
       layer_->layer_tree_impl()->IsActiveTree() ? ACTIVE_TREE : PENDING_TREE;
 
@@ -1546,6 +1555,10 @@ PictureLayerImpl::LayerEvictionTileIterator::LayerEvictionTileIterator(
       iteration_stage_(TilePriority::EVENTUALLY),
       required_for_activation_(false),
       layer_(layer) {
+  // Early out if the layer has no tilings.
+  // TODO(vmpstr): Once tile priorities are determined by the iterators, ensure
+  // that layers that don't have valid tile priorities have lowest priorities so
+  // they evict their tiles first (crbug.com/381704)
   if (!layer_->tilings_ || !layer_->tilings_->num_tilings())
     return;