Move code that doesn't depend on PPAPI out of remoting/client/plugin

remoting/client/plugin/normalizing_input_filter_mac.h

-// Copyright 2014 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 <map>
-
-#include "remoting/protocol/input_filter.h"
-
-namespace remoting {
-
-// NormalizingInputFilterMac is designed to solve the problem of missing keyup
-// events on Mac.
-//
-// PROBLEM
-//
-// On Mac if user presses CMD and then C key there is no keyup event generated
-// for C when user releases the C key before the CMD key.
-// The cause is that CMD + C triggers a system action and Chrome injects only a
-// keydown event for the C key. Safari shares the same behavior.
-//
-// SOLUTION
-//
-// When a keyup event for CMD key happens we will check all prior keydown
-// events received and inject corresponding keyup events artificially, with
-// the exception of:
-//
-// SHIFT, CONTROL, OPTION, LEFT CMD, RIGHT CMD and CAPS LOCK
-//
-// because they are reported by Chrome correctly.
-//
-// There are a couple cases that this solution doesn't work perfectly, one
-// of them leads to duplicated keyup events.
-//
-// User performs this sequence of actions:
-//
-// CMD DOWN, C DOWN, CMD UP, C UP
-//
-// In this case the algorithm will generate:
-//
-// CMD DOWN, C DOWN, C UP, CMD UP, C UP
-//
-// Because we artificially generate keyup events the C UP event is duplicated
-// as user releases the key after CMD key. This would not be a problem as the
-// receiver end will drop this duplicated keyup event.
-class NormalizingInputFilterMac : public protocol::InputFilter {
- public:
-  explicit NormalizingInputFilterMac(protocol::InputStub* input_stub);
-  ~NormalizingInputFilterMac() override;
-
-  // InputFilter overrides.
-  void InjectKeyEvent(const protocol::KeyEvent& event) override;
-
- private:
-  typedef std::map<int, protocol::KeyEvent> KeyPressedMap;
-
-  // Generate keyup events for any keys pressed with CMD.
-  void GenerateKeyupEvents();
-
-  // A map that stores pressed keycodes and the corresponding key event.
-  KeyPressedMap key_pressed_map_;
-
-  DISALLOW_COPY_AND_ASSIGN(NormalizingInputFilterMac);
-};
-
-}  // namespace remoting