Adds the UserInputMonitor implementation for Mac.

media/base/keyboard_event_counter.h

Index: media/base/keyboard_event_counter.h
diff --git a/media/base/keyboard_event_counter.h b/media/base/keyboard_event_counter.h
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+++ b/media/base/keyboard_event_counter.h
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+// 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.
+
+#ifndef MEDIA_BASE_KEYBOARD_EVENT_COUNTER_H_
+#define MEDIA_BASE_KEYBOARD_EVENT_COUNTER_H_
+
+#include <set>
+
+#include "base/synchronization/lock.h"
+#include "ui/base/events/event_constants.h"
+#include "ui/base/keycodes/keyboard_codes.h"
+
+namespace media {
+
+// This class tracks the total number of keypresses based on the OnKeyboardEvent
+// calls it receives from the client.
+// Multiple key down events for the same key are counted as one keypress until
+// the same key is released.
+// Thread safe.
+class KeyboardEventCounter {
+ public:
+  KeyboardEventCounter();
+  ~KeyboardEventCounter();
+
+  // Resets the count to 0.
+  void Reset();
+
+  // Returns the total number of keypresses since its creation or last Reset()
+  // call.
+  size_t GetKeyPressCount() const;
+
+  // The client should call this method on key down or key up events.
+  void OnKeyboardEvent(ui::EventType event, ui::KeyboardCode key_code);
+
+ private:
+  // "mutable" for GetKeyPressCount().
+  mutable base::Lock lock_;
+
+  // The set of keys currently held down.
+  std::set<ui::KeyboardCode> pressed_keys_;
+
+  size_t total_key_presses_;
+
+  DISALLOW_COPY_AND_ASSIGN(KeyboardEventCounter);
+};
+
+}  // namespace media
+
+#endif  // MEDIA_BASE_KEYBOARD_EVENT_COUNTER_H_