Add InputEventTimestampSource interface.

remoting/protocol/host_event_dispatcher.h

Index: remoting/protocol/host_event_dispatcher.h
diff --git a/remoting/protocol/host_event_dispatcher.h b/remoting/protocol/host_event_dispatcher.h
index 4c9df5e31f0c127ad23a3eeb131694cd399d12d9..de6a6062dce4dfa3c1a360afc01a09dcf6d43844 100644
--- a/remoting/protocol/host_event_dispatcher.h
+++ b/remoting/protocol/host_event_dispatcher.h
@@ -9,6 +9,7 @@
 
 #include "base/macros.h"
 #include "remoting/protocol/channel_dispatcher_base.h"
+#include "remoting/protocol/input_event_timestamps.h"
 
 namespace remoting {
 namespace protocol {
@@ -20,8 +21,6 @@ class InputStub;
 // channel to InputStub.
 class HostEventDispatcher : public ChannelDispatcherBase {
  public:
-  typedef base::Callback<void(int64_t)> OnInputEventCallback;
-
   HostEventDispatcher();
   ~HostEventDispatcher() override;
 
@@ -30,17 +29,14 @@ class HostEventDispatcher : public ChannelDispatcherBase {
   // the dispatcher.
   void set_input_stub(InputStub* input_stub) { input_stub_ = input_stub; }
 
-  // Set callback to notify of each message's sequence number. The
-  // callback cannot tear down this object.
-  void set_on_input_event_callback(const OnInputEventCallback& value) {
-    on_input_event_callback_ = value;
-  }
+  scoped_refptr<InputEventTimestampSource> GetEventTimestampSource();
 
  private:
   void OnIncomingMessage(std::unique_ptr<CompoundBuffer> buffer) override;
 
+  scoped_refptr<InputEventTimestampSourceImpl> event_timestamp_source_;
+
   InputStub* input_stub_ = nullptr;
-  OnInputEventCallback on_input_event_callback_;
 
   DISALLOW_COPY_AND_ASSIGN(HostEventDispatcher);
 };