Add a simple compositor for Sky

sky/compositor/surface_allocator.cc

+// 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.
+
+#include "sky/compositor/surface_allocator.h"
+
+#include "base/logging.h"
+
+namespace sky {
+
+SurfaceAllocator::SurfaceAllocator(uint32_t id_namespace)
+    : id_namespace_(id_namespace), next_id_(1) {
+  DCHECK(id_namespace);
+}
+
+SurfaceAllocator::~SurfaceAllocator() {
+}
+
+uint64_t SurfaceAllocator::CreateSurfaceId() {
+  // Surface IDs are 64 integers. The high 32 bits are the namespace of the ID,
+  // which is assigned to us by the surfaces service. The lower 32 bits are ours
+  // to allocate as we see fit. For simplicity, we just allocate them
+  // sequentially. In principle, we could run out, but at 60 Hz, it takes
+  // several years to run out.
+  return static_cast<uint64_t>(id_namespace_) << 32 | next_id_++;
+}
+
+}  // namespace sky