cc: Fix crash in MVRAR with missing recordings

cc/layers/picture_layer_impl_unittest.cc

 // Copyright 2013 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 <utility>
 
 #include "cc/layers/append_quads_data.h"
 #include "cc/layers/picture_layer.h"
@@ skipping 40 matching lines @@
   void SetupTrees(
       scoped_refptr<PicturePileImpl> pending_pile,
       scoped_refptr<PicturePileImpl> active_pile) {
     SetupPendingTree(active_pile);
     host_impl_.ActivatePendingTree();
 
     active_layer_ = static_cast<FakePictureLayerImpl*>(
         host_impl_.active_tree()->LayerById(id_));
 
     SetupPendingTree(pending_pile);
-    pending_layer_ = static_cast<FakePictureLayerImpl*>(
-        host_impl_.pending_tree()->LayerById(id_));
     pending_layer_->UpdateTwinLayer();
   }
 
   void AddDefaultTilingsWithInvalidation(const Region& invalidation) {
     active_layer_->AddTiling(2.3f);
     active_layer_->AddTiling(1.0f);
     active_layer_->AddTiling(0.5f);
     for (size_t i = 0; i < active_layer_->tilings()->num_tilings(); ++i)
       active_layer_->tilings()->tiling_at(i)->CreateAllTilesForTesting();
     pending_layer_->set_invalidation(invalidation);
     pending_layer_->SyncFromActiveLayer();
     for (size_t i = 0; i < pending_layer_->tilings()->num_tilings(); ++i)
       pending_layer_->tilings()->tiling_at(i)->CreateAllTilesForTesting();
   }
 
   void SetupPendingTree(
       scoped_refptr<PicturePileImpl> pile) {
     host_impl_.CreatePendingTree();
     LayerTreeImpl* pending_tree = host_impl_.pending_tree();
     // Clear recycled tree.
     pending_tree->DetachLayerTree();
 
     scoped_ptr<FakePictureLayerImpl> pending_layer =
         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(
       const PictureLayerTiling* tiling,
       PicturePileImpl* pile) {
     for (PictureLayerTiling::CoverageIterator
              iter(tiling, tiling->contents_scale(), tiling->ContentRect());
          iter;
          ++iter) {
       EXPECT_TRUE(*iter);
@@ skipping 700 matching lines @@
   AddDefaultTilingsWithInvalidation(invalidation);
 
   AppendQuadsData data;
   data.allow_tile_draw_quads = false;
   active_layer_->AppendQuads(&quad_culler, &data);
 
   ASSERT_EQ(1U, quad_culler.quad_list().size());
   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