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

cc/trees/occlusion.h

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CC_TREES_OCCLUSION_H_
+#define CC_TREES_OCCLUSION_H_
+
+#include "base/basictypes.h"
+#include "cc/base/cc_export.h"
+#include "cc/base/simple_enclosed_region.h"
+#include "ui/gfx/rect.h"

[danakj, 2014/09/09 22:11:59]

nit: can forward declare this

[vmpstr, 2014/09/10 00:32:24]

Done.

+#include "ui/gfx/transform.h"
+
+namespace cc {
+class LayerImpl;
+class Layer;
+template <typename LayerType>
+class OcclusionTracker;
+
+class CC_EXPORT Occlusion {
+ public:
+  Occlusion();
+
+  bool IsOccluded(const gfx::Rect& content_rect) const;
+
+ private:
+  friend class OcclusionTracker<Layer>;
+  friend class OcclusionTracker<LayerImpl>;
+
+  Occlusion(const gfx::Transform& draw_transform,

[danakj, 2014/09/09 22:11:59]

Mildly prefer making this public and remove friends. Tests will want to make
these objects too, for example.

[vmpstr, 2014/09/10 00:32:24]

Done.

+            const SimpleEnclosedRegion& occlusion_from_outside_target,
+            const SimpleEnclosedRegion& occlusion_from_inside_target);
+
+  gfx::Transform draw_transform_;
+  SimpleEnclosedRegion occlusion_from_outside_target_;
+  SimpleEnclosedRegion occlusion_from_inside_target_;
+};
+
+}  // namespace cc
+
+#endif  // CC_TREES_OCCLUSION_H_