cc: Replace Region with SimpleEnclosedRegion for occlusion tracking

cc/layers/layer.cc

Index: cc/layers/layer.cc
diff --git a/cc/layers/layer.cc b/cc/layers/layer.cc
index 57c055b7fea3576c25ab680009ad6efe46a4f9c6..63b9990d65faf0e9cb34cac442e7a2c03c44e08a 100644
--- a/cc/layers/layer.cc
+++ b/cc/layers/layer.cc
@@ -17,6 +17,7 @@
 #include "cc/animation/animation_registrar.h"
 #include "cc/animation/keyframed_animation_curve.h"
 #include "cc/animation/layer_animation_controller.h"
+#include "cc/base/simple_enclosed_region.h"
 #include "cc/layers/layer_client.h"
 #include "cc/layers/layer_impl.h"
 #include "cc/layers/scrollbar_layer_interface.h"
@@ -1179,10 +1180,10 @@ void Layer::RemoveLayerAnimationEventObserver(
   layer_animation_controller_->RemoveEventObserver(animation_observer);
 }
 
-Region Layer::VisibleContentOpaqueRegion() const {
+SimpleEnclosedRegion Layer::VisibleContentOpaqueRegion() const {
   if (contents_opaque())
-    return visible_content_rect();
-  return Region();
+    return SimpleEnclosedRegion(visible_content_rect());
+  return SimpleEnclosedRegion();
 }
 
 ScrollbarLayerInterface* Layer::ToScrollbarLayer() {