Add InputEventTimestampSource interface.

remoting/protocol/input_event_timestamps.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 REMOTING_PROTOCOL_INPUT_EVENT_TIMESTAMPS_H_
+#define REMOTING_PROTOCOL_INPUT_EVENT_TIMESTAMPS_H_
+
+#include "base/memory/ref_counted.h"
+#include "base/time/time.h"
+
+namespace remoting {
+namespace protocol {
+
+// Used on the host side to track timestamps for input events.
+struct InputEventTimestamps {
+  // Client-side timestamps. This value comesfrom the client clock, so it should

[Jamie, 2016/10/12 21:41:23]

Nit: missing space "comesfrom"

[Sergey Ulanov, 2016/10/14 19:34:26]

Done.

+  // not be used for any calculations on the host side (except in tests).
+  base::TimeTicks client_timestamp;
+
+  // Time when the event was received by the host.
+  base::TimeTicks host_timestamp;
+
+  bool is_null() { return client_timestamp.is_null(); }
+};
+
+// InputEventTimestampSource is used by VideoStream implementations to get event
+// timestamps that are sent back to the client as part of VideoStats message.
+class InputEventTimestampSource
+    : public base::RefCountedThreadSafe<InputEventTimestampSource> {
+ public:
+  InputEventTimestampSource() {}
+
+  virtual InputEventTimestamps GetLastEventTimestamps() = 0;
+
+ protected:
+  friend base::RefCountedThreadSafe<InputEventTimestampSource>;
+  virtual ~InputEventTimestampSource() {}
+};
+
+// Simple implementations of InputEventTimestampSource that just stores the
+// value provided to OnEventReceived().
+class InputEventTimestampSourceImpl : public InputEventTimestampSource {
+ public:
+  InputEventTimestampSourceImpl();
+
+  void OnEventReceived(InputEventTimestamps timestamps);
+
+  // InputEventTimestampSource implementation.
+  InputEventTimestamps GetLastEventTimestamps() override;
+
+ protected:
+  ~InputEventTimestampSourceImpl() override;
+
+ private:
+  InputEventTimestamps last_timestamps_;
+};
+
+}  // namespace protocol
+}  // namespace remoting
+
+#endif  // REMOTING_PROTOCOL_INPUT_EVENT_TIMESTAMPS_H_