cc: Make the PictureLayerImpl raster source null until commit.

cc/trees/layer_tree_host_impl_unittest.cc

Index: cc/trees/layer_tree_host_impl_unittest.cc
diff --git a/cc/trees/layer_tree_host_impl_unittest.cc b/cc/trees/layer_tree_host_impl_unittest.cc
index c8e27a90ab7c6e552464ec40c3e5731bfd8c8297..0b3928772a71e8000ab157f4c1818ff6ad220b30 100644
--- a/cc/trees/layer_tree_host_impl_unittest.cc
+++ b/cc/trees/layer_tree_host_impl_unittest.cc
@@ -7794,8 +7794,18 @@ TEST_F(LayerTreeHostImplTest, ScrollAnimated) {
 
 TEST_F(LayerTreeHostImplTest, GetPictureLayerImplPairs) {
   host_impl_->CreatePendingTree();
-  host_impl_->pending_tree()->SetRootLayer(
-      PictureLayerImpl::Create(host_impl_->pending_tree(), 10, false));
+
+  scoped_ptr<PictureLayerImpl> layer =
+      PictureLayerImpl::Create(host_impl_->pending_tree(), 10, false);
+  layer->SetBounds(gfx::Size(10, 10));
+
+  scoped_refptr<RasterSource> pile(FakePicturePileImpl::CreateEmptyPile(
+      gfx::Size(10, 10), gfx::Size(10, 10)));
+  Region empty_invalidation;
+  const PictureLayerTilingSet* null_tiling_set = nullptr;
+  layer->UpdateRasterSource(pile, &empty_invalidation, null_tiling_set);
+
+  host_impl_->pending_tree()->SetRootLayer(layer.Pass());
 
   LayerTreeImpl* pending_tree = host_impl_->pending_tree();
   LayerImpl* pending_layer = pending_tree->root_layer();