cc: Do not cleanup tiles with raster tasks.

cc/resources/picture_layer_tiling.cc

Index: cc/resources/picture_layer_tiling.cc
diff --git a/cc/resources/picture_layer_tiling.cc b/cc/resources/picture_layer_tiling.cc
index fdfbad9f62e3e60bbd1949541123ef36c5713de1..5d29583f205254311b23201442177552d51e0373 100644
--- a/cc/resources/picture_layer_tiling.cc
+++ b/cc/resources/picture_layer_tiling.cc
@@ -94,6 +94,10 @@ PictureLayerTiling::PictureLayerTiling(float contents_scale,
 }
 
 PictureLayerTiling::~PictureLayerTiling() {
+  // Reset priority as tile is ref-counted and might still be used
+  // even though we no longer hold a reference to it here anymore.
+  for (TileMap::const_iterator it = tiles_.begin(); it != tiles_.end(); ++it)
+    it->second.get()->SetPriority(client_->GetTree(), TilePriority());
 }
 
 void PictureLayerTiling::SetClient(PictureLayerTilingClient* client) {
@@ -214,6 +218,11 @@ void PictureLayerTiling::DoInvalidate(const Region& layer_region,
       TileMap::iterator find = tiles_.find(key);
       if (find == tiles_.end())
         continue;
+
+      // Reset priority as tile is ref-counted and might still be used
+      // even though we no longer hold a reference to it here anymore.
+      find->second.get()->SetPriority(client_->GetTree(), TilePriority());
+
       tiles_.erase(find);
       new_tile_keys.push_back(key);
     }
@@ -598,8 +607,12 @@ void PictureLayerTiling::SetLiveTilesRect(
     TileMap::iterator found = tiles_.find(key);
     // If the tile was outside of the recorded region, it won't exist even
     // though it was in the live rect.
-    if (found != tiles_.end())
+    if (found != tiles_.end()) {
+      // Reset priority as tile is ref-counted and might still be used
+      // even though we no longer hold a reference to it here anymore.
+      found->second.get()->SetPriority(client_->GetTree(), TilePriority());
       tiles_.erase(found);
+    }
   }
 
   const PictureLayerTiling* twin_tiling = client_->GetTwinTiling(this);