Initial attempt at counting layers in the compositor thread.

cc/trees/layer_tree_impl_unittest.cc

Index: cc/trees/layer_tree_impl_unittest.cc
diff --git a/cc/trees/layer_tree_impl_unittest.cc b/cc/trees/layer_tree_impl_unittest.cc
index 9edf838bb60c3379ffe76fc01943a19ac3dc5e22..ce44a7cc430a68e3527c89e9c393ee8c1d8671c5 100644
--- a/cc/trees/layer_tree_impl_unittest.cc
+++ b/cc/trees/layer_tree_impl_unittest.cc
@@ -2319,5 +2319,24 @@ TEST_F(LayerTreeImplTest, SelectionBoundsForScaledLayers) {
   EXPECT_TRUE(right_output.visible);
 }
 
+TEST_F(LayerTreeImplTest, NumLayersTestZero) {
+  CHECK_EQ(0u, host_impl().active_tree()->NumLayers());
+}
+
+TEST_F(LayerTreeImplTest, NumLayersTestOne) {
+  scoped_ptr<LayerImpl> root = LayerImpl::Create(host_impl().active_tree(), 1);
+  host_impl().active_tree()->SetRootLayer(root.Pass());
+  CHECK_EQ(1u, host_impl().active_tree()->NumLayers());
+}
+
+TEST_F(LayerTreeImplTest, NumLayersSmallTree) {
+  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));
+  host_impl().active_tree()->SetRootLayer(root.Pass());
+  EXPECT_EQ(4u, host_impl().active_tree()->NumLayers());
+}
+
 }  // namespace
 }  // namespace cc