Connect to DesktopEnvironment's stubs only when audio/video schedulers are about to be created.

remoting/protocol/input_event_tracker.h

 // Copyright (c) 2012 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_TRACKER_H_
 #define REMOTING_PROTOCOL_INPUT_EVENT_TRACKER_H_
 
 #include <set>
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "remoting/protocol/input_stub.h"
 #include "third_party/skia/include/core/SkPoint.h"
 
 namespace remoting {
 namespace protocol {
 
 // Filtering InputStub which tracks mouse and keyboard input events before
 // passing them on to |input_stub|, and can dispatch release events to
 // |input_stub| for all currently-pressed keys and buttons when necessary.
 class InputEventTracker : public InputStub {
  public:
-  explicit InputEventTracker(protocol::InputStub* input_stub);
+  explicit InputEventTracker(InputStub* input_stub);
   virtual ~InputEventTracker();
 
+  // Sets the InputStub that sends events to the client.
+  void set_input_stub(InputStub* input_stub) { input_stub_ = input_stub; }

[Wez, 2013/01/08 18:34:00]

Why not derived from InputFilter to get this, and replace input_stub->Foo()
calls w/ InputFilter::Foo()?

[Wez, 2013/01/08 18:34:00]

The problem with this is that it creates the question of the InputEventTracker's
semantics when |input_stub| is null. If you instead just add an InputFilter in
ClientSession, to pass to the InputEventTracker, then that becomes
ClientSession's problem, and ClientSession is in a position to arrange the right
release / NULLify ordering. 

[alexeypa (please no reviews), 2013/01/08 20:00:14]

Done.

+
   // Returns true if the key with the specified USB code is currently pressed.
   bool IsKeyPressed(uint32 usb_keycode) const;
 
   // Returns the count of keys currently pressed.
   int PressedKeyCount() const;
 
   // Dispatch release events for all currently-pressed keys and mouse buttons
   // to the InputStub.
   void ReleaseAll();
 
   // InputStub interface.
   virtual void InjectKeyEvent(const KeyEvent& event) OVERRIDE;
   virtual void InjectMouseEvent(const MouseEvent& event) OVERRIDE;
 
  private:
   protocol::InputStub* input_stub_;
 
   std::set<uint32> pressed_keys_;
 
   SkIPoint mouse_pos_;
   uint32 mouse_button_state_;
 
   DISALLOW_COPY_AND_ASSIGN(InputEventTracker);
 };
 
 }  // namespace protocol
 }  // namespace remoting
 
 #endif  // REMOTING_PROTOCOL_INPUT_EVENT_TRACKER_H_