cc: Fix crash in MVRAR with missing recordings

cc/layers/picture_layer_impl_unittest.cc

Index: cc/layers/picture_layer_impl_unittest.cc
diff --git a/cc/layers/picture_layer_impl_unittest.cc b/cc/layers/picture_layer_impl_unittest.cc
index d67ea46232570f3714228ae5e8967d6c1dd39217..0695ba1c28c4ce191ca11a818a616cd87576d421 100644
--- a/cc/layers/picture_layer_impl_unittest.cc
+++ b/cc/layers/picture_layer_impl_unittest.cc
@@ -58,8 +58,6 @@ class PictureLayerImplTest : public testing::Test {
         host_impl_.active_tree()->LayerById(id_));
 
     SetupPendingTree(pending_pile);
-    pending_layer_ = static_cast<FakePictureLayerImpl*>(
-        host_impl_.pending_tree()->LayerById(id_));
     pending_layer_->UpdateTwinLayer();
   }
 
@@ -86,6 +84,9 @@ class PictureLayerImplTest : public testing::Test {
         FakePictureLayerImpl::CreateWithPile(pending_tree, id_, pile);
     pending_layer->SetDrawsContent(true);
     pending_tree->SetRootLayer(pending_layer.PassAs<LayerImpl>());
+
+    pending_layer_ = static_cast<FakePictureLayerImpl*>(
+        host_impl_.pending_tree()->LayerById(id_));
   }
 
   static void VerifyAllTilesExistAndHavePile(
@@ -806,5 +807,25 @@ TEST_F(PictureLayerImplTest, DisallowTileDrawQuads) {
   EXPECT_EQ(DrawQuad::PICTURE_CONTENT, quad_culler.quad_list()[0]->material);
 }
 
+TEST_F(PictureLayerImplTest, MarkRequiredNullTiles) {
+  gfx::Size tile_size(100, 100);
+  gfx::Size layer_bounds(1000, 1000);
+
+  scoped_refptr<FakePicturePileImpl> pending_pile =
+      FakePicturePileImpl::CreateEmptyPile(tile_size, layer_bounds);
+  // Layers with entirely empty piles can't get tilings.
+  pending_pile->AddRecordingAt(0, 0);

[danakj, 2013/05/29 00:11:47]

From holiday: do you need to add recording? Or could you just not do anything
here?

[enne (OOO), 2013/05/29 00:14:29]

Yes.  CanHaveTilings() is false if the pile's recorded region is empty.

[danakj, 2013/05/29 10:39:34]

I see. I guess its just nonobvious that there are in fact null tiles being hit
from reading the test alone. Or that UpdateDrawProps didn't just early out or
something. 

+
+  SetupPendingTree(pending_pile);
+
+  ASSERT_TRUE(pending_layer_->CanHaveTilings());
+  pending_layer_->AddTiling(1.0f);
+  pending_layer_->AddTiling(2.0f);
+
+  // It should be safe to call this (and MarkVisibleResourcesAsRequired)

[danakj, 2013/05/29 00:11:47]

Can you verify that the tilings were not added? Num_tilings is 0 or something?

[enne (OOO), 2013/05/29 00:14:29]

The tilings are supposed to be there, it's that the tiles aren't.  Are you
asking that I verify that iterating over each tiling has both null and non-null
tiles?

[danakj, 2013/05/29 10:39:34]

Oh sorry, right.

+  // on a layer with no recordings.
+  host_impl_.pending_tree()->UpdateDrawProperties();
+}
+
 }  // namespace
 }  // namespace cc