Add DisplayCompositorTest.

cc/surfaces/surface_reference_manager.h

Index: cc/surfaces/surface_reference_manager.h
diff --git a/cc/surfaces/surface_reference_manager.h b/cc/surfaces/surface_reference_manager.h
new file mode 100644
index 0000000000000000000000000000000000000000..66d55c67a4e96f703ed131bd4341537b90802808
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+++ b/cc/surfaces/surface_reference_manager.h
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+// Copyright 2016 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_SURFACES_SURFACE_REFERENCE_MANAGER_H_
+#define CC_SURFACES_SURFACE_REFERENCE_MANAGER_H_
+
+namespace cc {
+
+class SurfaceId;
+
+// Interface to manage surface references.
+class SurfaceReferenceManager {
+ public:
+  // Returns the top level root SurfaceId. Surfaces that are not reachable
+  // from the top level root may be garbage collected. It will not be a valid
+  // SurfaceId and will never correspond to a surface.
+  virtual const SurfaceId& GetRootSurfaceId() const = 0;
+
+  // Adds a reference from a parent surface to a child surface. Any surface
+  // embedding a child surface should have a reference added so that the child
+  // surface is not garbage collected until after the parent surface.
+  virtual void AddSurfaceReference(const SurfaceId& parent_id,
+                                   const SurfaceId& child_id) = 0;
+
+  // Removes a reference from a parent surface to a child surface.
+  virtual void RemoveSurfaceReference(const SurfaceId& parent_id,
+                                      const SurfaceId& child_id) = 0;
+
+  // Returns the number of surfaces that have references to |surface_id|. When
+  // the count is zero nothing is referencing the surface and it may be garbage
+  // collected.
+  virtual size_t GetSurfaceReferenceCount(
+      const SurfaceId& surface_id) const = 0;
+
+  // Returns the number of surfaces that |surface_id| has references to.
+  virtual size_t GetReferencedSurfaceCount(
+      const SurfaceId& surface_id) const = 0;
+
+ protected:
+  virtual ~SurfaceReferenceManager() {}
+};
+
+}  // namespace cc
+
+#endif  // CC_SURFACES_SURFACE_REFERENCE_MANAGER_H_