Adds the UserInputMonitor implementation for Mac.

media/base/user_input_monitor.cc

 // Copyright 2013 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 "media/base/user_input_monitor.h"
 
 #include "third_party/skia/include/core/SkPoint.h"
 
 namespace media {
 
@@ skipping 53 matching lines @@
 void UserInputMonitor::OnMouseEvent(const SkIPoint& position) {
   base::AutoLock auto_lock(lock_);
   FOR_EACH_OBSERVER(
       MouseEventListener, mouse_listeners_, OnMouseMoved(position));
 }
 
 void UserInputMonitor::OnKeyboardEvent(ui::EventType event,
                                        ui::KeyboardCode key_code) {
   base::AutoLock auto_lock(lock_);
   // Updates the pressed keys and maybe notifies the key_stroke_listeners_.
+  // The Mac implementation does not listen to the the key down/up events, but
+  // polls the key state and only notifies UserInputMonitor when a key is down
+  // now but not in the previous polling. So we do not check/update
+  // |pressed_keys_| here.
   if (event == ui::ET_KEY_PRESSED) {
+#if !defined(OS_MACOSX)
     if (pressed_keys_.find(key_code) != pressed_keys_.end())
       return;
     pressed_keys_.insert(key_code);
+#endif
+
     DVLOG(6) << "Key stroke detected.";
     FOR_EACH_OBSERVER(KeyStrokeListener, key_stroke_listeners_, OnKeyStroke());
   } else {
+#if defined(OS_MACOSX)
+    NOTREACHED();
+    return;
+#endif
+
     DCHECK_EQ(ui::ET_KEY_RELEASED, event);
     DCHECK(pressed_keys_.find(key_code) != pressed_keys_.end());
     pressed_keys_.erase(key_code);
   }
 }
 
 }  // namespace media