wip: not for commit (update twin relationship)

cc/layers/picture_layer_impl.cc

 // Copyright 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/layers/picture_layer_impl.h"
 
 #include <algorithm>
 #include <limits>
 
 #include "base/debug/trace_event_argument.h"
@@ skipping 925 matching lines @@
   return twin_had_missing_tile;
 }
 
 void PictureLayerImpl::DoPostCommitInitialization() {
   DCHECK(needs_post_commit_initialization_);
   DCHECK(layer_tree_impl()->IsPendingTree());
 
   if (!tilings_)
     tilings_.reset(new PictureLayerTilingSet(this, bounds()));
 
-  DCHECK(!twin_layer_);
-  twin_layer_ = static_cast<PictureLayerImpl*>(
-      layer_tree_impl()->FindActiveTreeLayerById(id()));
   if (twin_layer_) {
-    DCHECK(!twin_layer_->twin_layer_);
-    twin_layer_->twin_layer_ = this;
     // If the twin has never been pushed to, do not sync from it.
     // This can happen if this function is called during activation.
     if (!twin_layer_->needs_post_commit_initialization_)
       SyncFromActiveLayer(twin_layer_);
   }
 
   needs_post_commit_initialization_ = false;
 }
 
+void PictureLayerImpl::UpdateTwinRelationship() {
+  DCHECK(!twin_layer_);
+  twin_layer_ = static_cast<PictureLayerImpl*>(
+      layer_tree_impl()->FindActiveTreeLayerById(id()));
+  if (twin_layer_) {
+    DCHECK(!twin_layer_->twin_layer_);
+    twin_layer_->twin_layer_ = this;
+  }
+}
+
 PictureLayerTiling* PictureLayerImpl::AddTiling(float contents_scale) {
   DCHECK(CanHaveTilingWithScale(contents_scale)) <<
       "contents_scale: " << contents_scale;
 
   PictureLayerTiling* tiling = tilings_->AddTiling(contents_scale);
 
   DCHECK(pile_->HasRecordings());
 
   if (twin_layer_)
     twin_layer_->SyncTiling(tiling);
@@ skipping 780 matching lines @@
       PictureLayerTilingSet::TilingRange tiling_range = CurrentTilingRange();
       size_t current_tiling_range_offset = current_tiling_ - tiling_range.start;
       return tiling_range.end - 1 - current_tiling_range_offset;
     }
   }
   NOTREACHED();
   return 0;
 }
 
 }  // namespace cc