Initial attempt at counting layers in the compositor thread.

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 9f2a5a2fba0e08a42a81d104ac7bd29a86eb1297..079fc9d124f07420aeea5837da9bbb2951222c99 100644
--- a/cc/trees/layer_tree_host_impl_unittest.cc
+++ b/cc/trees/layer_tree_host_impl_unittest.cc
@@ -6723,5 +6723,56 @@ TEST_F(LayerTreeHostImplTest, ExternalTransformReflectedInNextDraw) {
       external_transform, layer->draw_properties().target_space_transform);
 }
 
+TEST_F(LayerTreeHostImplTest, TestLayerCountingZeroInit) {

[Ian Vollick, 2014/07/10 03:16:23]

Nice tests!

[dneto, 2014/07/10 18:44:17]

Thanks, but obviated by danakj's suggestion. :-)

+  EXPECT_EQ(0u, host_impl_->num_layers_for_testing());
+}
+
+TEST_F(LayerTreeHostImplTest, TestLayerCountingRootOnly) {
+  scoped_ptr<LayerImpl> root = LayerImpl::Create(host_impl_->active_tree(), 1);
+  SetupRootLayerImpl(root.Pass());
+  DrawFrame();
+  EXPECT_EQ(1u, host_impl_->num_layers_for_testing());
+}
+
+TEST_F(LayerTreeHostImplTest, TestLayerCountingSmallTree) {
+  scoped_ptr<LayerImpl> root = LayerImpl::Create(host_impl_->active_tree(), 1);
+  root->AddChild(LayerImpl::Create(host_impl_->active_tree(), 2));
+  root->AddChild(LayerImpl::Create(host_impl_->active_tree(), 3));
+  root->child_at(1)->AddChild(LayerImpl::Create(host_impl_->active_tree(), 4));
+  SetupRootLayerImpl(root.Pass());
+  DrawFrame();
+  EXPECT_EQ(4u, host_impl_->num_layers_for_testing());
+}
+
+TEST_F(LayerTreeHostImplTest, TestLayerCountingWithSequenceOfTrees) {
+  // The first tree has two nodes.
+  scoped_ptr<LayerImpl> root0 = LayerImpl::Create(host_impl_->active_tree(), 1);
+  root0->AddChild(LayerImpl::Create(host_impl_->active_tree(), 2));
+  SetupRootLayerImpl(root0.Pass());
+  DrawFrame();
+  EXPECT_EQ(2u, host_impl_->num_layers_for_testing());
+
+  // We haven't changed anything.  The count should stay the same.
+  // In particular the count should not accumulate.
+  DrawFrame();
+  EXPECT_EQ(2u, host_impl_->num_layers_for_testing());
+
+  // Set a new tree, with just a root.
+  // Should have a lower count now.
+  host_impl_->ResetTreesForTesting();
+  scoped_ptr<LayerImpl> root1 = LayerImpl::Create(host_impl_->active_tree(), 1);
+  SetupRootLayerImpl(root1.Pass());
+  DrawFrame();
+  EXPECT_EQ(1u, host_impl_->num_layers_for_testing());
+
+  // And it should go back up when we use a tree with more nodes.
+  host_impl_->ResetTreesForTesting();
+  scoped_ptr<LayerImpl> root2 = LayerImpl::Create(host_impl_->active_tree(), 1);
+  root2->AddChild(LayerImpl::Create(host_impl_->active_tree(), 2));
+  SetupRootLayerImpl(root2.Pass());
+  DrawFrame();
+  EXPECT_EQ(2u, host_impl_->num_layers_for_testing());
+}
+
 }  // namespace
 }  // namespace cc