Reland of: cc: Add occlusion checker as a fixed view of occlusion tracker.

cc/trees/occlusion_tracker_unittest.cc

Index: cc/trees/occlusion_tracker_unittest.cc
diff --git a/cc/trees/occlusion_tracker_unittest.cc b/cc/trees/occlusion_tracker_unittest.cc
index aaf655f2a7f409ff277bd60dfe83f7fe03243572..56059cb0e98f9520fc9e2970f2cc6b5ced7a59b1 100644
--- a/cc/trees/occlusion_tracker_unittest.cc
+++ b/cc/trees/occlusion_tracker_unittest.cc
@@ -85,6 +85,11 @@ class TestOcclusionTrackerWithClip : public TestOcclusionTracker<LayerType> {
   bool OccludedLayer(const LayerType* layer,
                      const gfx::Rect& content_rect) const {
     DCHECK(layer->visible_content_rect().Contains(content_rect));
+    EXPECT_EQ(
+        this->Occluded(
+            layer->render_target(), content_rect, layer->draw_transform()),
+        this->GetCurrentOcclusionForLayer(layer->draw_transform())
+            .IsOccluded(content_rect));
     return this->Occluded(
         layer->render_target(), content_rect, layer->draw_transform());
   }