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

cc/trees/occlusion_tracker.cc

Index: cc/trees/occlusion_tracker.cc
diff --git a/cc/trees/occlusion_tracker.cc b/cc/trees/occlusion_tracker.cc
index f233e074a9ba8b0a1441658ad2751ec3dbd907af..cdecb17af6d0afd80cad437f19108dabed66e678 100644
--- a/cc/trees/occlusion_tracker.cc
+++ b/cc/trees/occlusion_tracker.cc
@@ -28,6 +28,23 @@ template <typename LayerType>
 OcclusionTracker<LayerType>::~OcclusionTracker() {}
 
 template <typename LayerType>
+OcclusionChecker<LayerType>
+OcclusionTracker<LayerType>::GenerateOcclusionChecker(
+    const gfx::Transform& draw_transform) const {
+  if (stack_.empty())

[danakj, 2014/09/09 15:14:39]

DCHECK this instead

[vmpstr, 2014/09/09 21:56:56]

Done.

+    return OcclusionChecker<LayerType>();
+
+  const StackObject& back = stack_.back();
+  if (back.occlusion_from_inside_target.IsEmpty() &&
+      back.occlusion_from_outside_target.IsEmpty()) {
+    return OcclusionChecker<LayerType>();

[danakj, 2014/09/09 15:14:39]

I'm not sure I see the point of this early out. What does it do for us?

[vmpstr, 2014/09/09 21:56:56]

Not much :) I removed it.

+  }
+  return OcclusionChecker<LayerType>(draw_transform,
+                                     back.occlusion_from_outside_target,
+                                     back.occlusion_from_inside_target);
+}
+
+template <typename LayerType>
 void OcclusionTracker<LayerType>::EnterLayer(
     const LayerIteratorPosition<LayerType>& layer_iterator) {
   LayerType* render_target = layer_iterator.target_render_surface_layer;