cc: Always keep the PictureLayerImpl::twin_layer_ pointer valid.

cc/test/fake_picture_layer_tiling_client.cc

Index: cc/test/fake_picture_layer_tiling_client.cc
diff --git a/cc/test/fake_picture_layer_tiling_client.cc b/cc/test/fake_picture_layer_tiling_client.cc
index ce46c917615fb04a15275c2f8c1b9e5668676877..bb0da0c0036caa0d8032542e29ee5b154ab1812d 100644
--- a/cc/test/fake_picture_layer_tiling_client.cc
+++ b/cc/test/fake_picture_layer_tiling_client.cc
@@ -77,8 +77,9 @@ const Region* FakePictureLayerTilingClient::GetInvalidation() {
   return &invalidation_;
 }
 
-const PictureLayerTiling* FakePictureLayerTilingClient::GetTwinTiling(
-      const PictureLayerTiling* tiling) const {
+const PictureLayerTiling*
+FakePictureLayerTilingClient::GetPendingOrActiveTwinTiling(
+    const PictureLayerTiling* tiling) const {
   return twin_tiling_;
 }