[Do not submit] D3DKMTWaitForVerticalBlankEvent VSync prototype

content/browser/compositor/gpu_vsync_begin_frame_source.h

+// 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 CONTENT_BROWSER_COMPOSITOR_GPU_VSYNC_BEGIN_FRAME_SOURCE_H_
+#define CONTENT_BROWSER_COMPOSITOR_GPU_VSYNC_BEGIN_FRAME_SOURCE_H_
+
+#include "base/memory/weak_ptr.h"
+#include "base/time/time.h"
+#include "cc/scheduler/begin_frame_source.h"
+
+namespace content {
+
+class GpuVSyncControl {
+ public:
+  virtual void EnableVSync(bool enabled) = 0;
+};
+
+// TODO: this should derive from ExternalBeginFrameSource but existing
+// implementation of gpu_process_transport_factory makes it difficult.
+// Therefore the current solution is to duplicate some of
+// ExternalBeginFrameSource implementation here.
+class GpuVSyncBeginFrameSource : public cc::SyntheticBeginFrameSource {
+ public:
+  explicit GpuVSyncBeginFrameSource(GpuVSyncControl* vsync_control);
+  ~GpuVSyncBeginFrameSource() override;
+
+  // cc::BeginFrameSource implementation.
+  void AddObserver(cc::BeginFrameObserver* obs) override;
+  void RemoveObserver(cc::BeginFrameObserver* obs) override;
+  void DidFinishFrame(cc::BeginFrameObserver* obs,
+                      const cc::BeginFrameAck& ack) override;
+  bool IsThrottled() const override;
+
+  // cc::SyntheticBeginFrameSource implementation.
+  void OnUpdateVSyncParameters(base::TimeTicks timebase,
+                               base::TimeDelta interval) override;
+  void SetAuthoritativeVSyncInterval(base::TimeDelta interval) override;
+
+ private:
+  void OnBeginFrame(const cc::BeginFrameArgs& args);
+  static void OnBeginFrame(cc::BeginFrameObserver* obs,
+                           const cc::BeginFrameArgs& args);
+  void EnableVSync(bool enabled);
+
+  GpuVSyncControl* const vsync_control_;
+  bool enabled_;
+  uint64_t next_sequence_number_;
+  cc::BeginFrameArgs previous_begin_frame_args_;
+  std::unordered_set<cc::BeginFrameObserver*> observers_;
+
+  DISALLOW_COPY_AND_ASSIGN(GpuVSyncBeginFrameSource);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_COMPOSITOR_GPU_VSYNC_BEGIN_FRAME_SOURCE_H_