[chromoting] Fix sticky c key with cmd on mac using usb keycode

remoting/client/plugin/mac_key_event_processor.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.
 
 // MacKeyEventProcessor 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.
 //
-// This is a list of sample edge cases:
-//
-// CMD DOWN, C DOWN, C UP, CMD UP
-// CMD DOWN, SHIFT DOWN, C DOWN, C UP, CMD UP, SHIFT UP
-// CMD DOWN, CAPS LOCK DOWN, CMD DOWN, CAPS LOCK DOWN
-// L CMD DOWN, C DOWN, R CMD DOWN, L CMD UP, C UP, R CMD UP
-//
 // 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.
+// as user releases the key after CMD key. This would not be a problem as the
+// receiver end will drop this duplicated keyup event.
 
 #ifndef REMOTING_CLIENT_PLUGIN_MAC_KEY_EVENT_PROCESSOR_H_
 #define REMOTING_CLIENT_PLUGIN_MAC_KEY_EVENT_PROCESSOR_H_
 
 #include <map>
 
 #include "base/basictypes.h"
 #include "remoting/proto/event.pb.h"
 #include "remoting/protocol/input_filter.h"
 
 namespace remoting {
 
 namespace protocol {
 class InputStub;
 }  // namespace protocol
 
 class MacKeyEventProcessor : public protocol::InputFilter {
  public:
   explicit MacKeyEventProcessor(protocol::InputStub* input_stub);
   virtual ~MacKeyEventProcessor();
 
   // InputFilter overrides.
   virtual void InjectKeyEvent(const protocol::KeyEvent& event) OVERRIDE;
 
-  // Return the number of keys pressed. This method is used by unit test to
-  // test correctness of this class.
-  int NumberOfPressedKeys() const;
-
  private:
-  // Iterate the current pressed keys and generate keyup events.
+  // Generate keyup events for any keys pressed with CMD.
   void GenerateKeyupEvents();
 
   // A map that stores pressed keycodes and the corresponding key event.
   typedef std::map<int, protocol::KeyEvent> KeyPressedMap;
   KeyPressedMap key_pressed_map_;
 
   DISALLOW_COPY_AND_ASSIGN(MacKeyEventProcessor);
 };
 
 }  // namespace remoting
 
 #endif  // REMOTING_CLIENT_PLUGIN_MAC_KEY_EVENT_PROCESSOR_H_