Add InputEventTimestampSource interface.

remoting/protocol/input_event_timestamps.cc

+// 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.
+
+#include "remoting/protocol/input_event_timestamps.h"
+
+namespace remoting {
+namespace protocol {
+
+InputEventTimestampSourceImpl::InputEventTimestampSourceImpl() {}
+InputEventTimestampSourceImpl::~InputEventTimestampSourceImpl() {}
+
+void InputEventTimestampSourceImpl::OnEventReceived(
+    InputEventTimestamps timestamps) {
+  last_timestamps_ = timestamps;
+}
+
+InputEventTimestamps InputEventTimestampSourceImpl::GetLastEventTimestamps() {
+  InputEventTimestamps result = last_timestamps_;
+  last_timestamps_ = InputEventTimestamps();

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

Why reset this here? It makes GetLastEventTimestamps non-idempotent, and it's
not obvious from the interface description why you'd want that.

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

Renamed the function to TakeLastEventTimestamps() and added a comment in the
header to explain how it supposed to work.

+  return result;
+}
+
+}  // namespace protocol
+}  // namespace remoting