Bug 1476368 - Avoid moving picture primitives when destroying them. r=gw

--HG--
extra : source : 88f409bc495a135764d75ac22802c2fca94d7be3
extra : histedit_source : fa57c05c5227b676ba5f7c582c00b6d1511d89be

gfx/wr/webrender/src/picture.rs

@@ -2266,7 +2266,7 @@ impl PicturePrimitive {
     /// gives a picture a chance to retain any cached tiles that
     /// may be useful during the next scene build.
     pub fn destroy(
-        mut self,
+        &mut self,
         retained_tiles: &mut RetainedTiles,
         clip_scroll_tree: &ClipScrollTree,
     ) {
@@ -2279,9 +2279,7 @@ impl PicturePrimitive {
                 clip_scroll_tree,
             );
 
-            for tile in tile_cache.tiles {
-                retained_tiles.tiles.push(tile);
-            }
+            retained_tiles.tiles.extend(tile_cache.tiles);
         }
     }
 

gfx/wr/webrender/src/prim_store/mod.rs

@@ -1700,11 +1700,11 @@ impl PrimitiveStore {
     /// Destroy an existing primitive store. This is called just before
     /// a primitive store is replaced with a newly built scene.
     pub fn destroy(
-        self,
+        mut self,
         retained_tiles: &mut RetainedTiles,
         clip_scroll_tree: &ClipScrollTree,
     ) {
-        for pic in self.pictures {
+        for pic in &mut self.pictures {
             pic.destroy(
                 retained_tiles,
                 clip_scroll_tree,