Chromium roll (https://codereview.chromium.org/976353002)

cc/resources/picture_layer_tiling_set.h

Index: cc/resources/picture_layer_tiling_set.h
diff --git a/cc/resources/picture_layer_tiling_set.h b/cc/resources/picture_layer_tiling_set.h
index fc1e581f5e88ba458a270881abd5367ca1b27bb0..a4c2fd8a1eff633f5edfde796c84d802aa1fef6d 100644
--- a/cc/resources/picture_layer_tiling_set.h
+++ b/cc/resources/picture_layer_tiling_set.h
@@ -55,9 +55,15 @@ class CC_EXPORT PictureLayerTilingSet {
                       PictureLayerTilingSet* recycled_twin_set);
   void RemoveNonIdealTilings();
 
+  // This function can be called on both the active and pending tree.
+  // |pending_twin_set| represents the current pending twin. In situations where
+  // this is called on the active tree in two trees situations,
+  // |pending_twin_set| represents the tiling set from the pending twin layer.
+  // In situations where this is called on the sync tree (whether it's pending
+  // or active in cases of one tree), |pending_twin_set| should be nullptr.
   void UpdateTilingsToCurrentRasterSource(
       scoped_refptr<RasterSource> raster_source,
-      const PictureLayerTilingSet* twin_set,
+      const PictureLayerTilingSet* pending_twin_set,
       const Region& layer_invalidation,
       float minimum_contents_scale,
       float maximum_contents_scale);
@@ -163,6 +169,10 @@ class CC_EXPORT PictureLayerTilingSet {
       float skewport_target_time_in_seconds,
       int skewport_extrapolation_limit_in_content_pixels);
 
+  void CopyTilingsFromPendingTwin(
+      const PictureLayerTilingSet* pending_twin_set,
+      const scoped_refptr<RasterSource>& raster_source);
+
   // Remove one tiling.
   void Remove(PictureLayerTiling* tiling);