Adds the UserInputMonitor implementation for Mac.

media/base/user_input_monitor.h

Index: media/base/user_input_monitor.h
diff --git a/media/base/user_input_monitor.h b/media/base/user_input_monitor.h
index 9eb82f334f833612a0720367c83c4513ba275bef..d3854640c497cb5c5733b3f7021ac54441ae0f64 100644
--- a/media/base/user_input_monitor.h
+++ b/media/base/user_input_monitor.h
@@ -9,7 +9,6 @@
 
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
-#include "base/memory/weak_ptr.h"
 #include "base/observer_list.h"
 #include "base/synchronization/lock.h"
 #include "media/base/media_export.h"
@@ -28,6 +27,8 @@ namespace media {
 // Thread safe. The thread on which the listenters are called is not guaranteed.
 // The callers should not perform expensive/blocking tasks in the callback since
 // it might be called on the browser UI/IO threads.
+// The object must outlive the browser UI/IO threads to make sure the callbacks
+// will not access deleted object.
 class MEDIA_EXPORT UserInputMonitor {
  public:
   // The interface to receive mouse movement events.
@@ -89,7 +90,7 @@ class MEDIA_EXPORT UserInputMonitor {
   bool monitoring_keyboard_;
   // The set of keys currently held down. Used for convering raw keyboard events
   // into KeyStrokeListener callbacks.
-  std::set<ui::KeyboardCode> pressed_keys_;
+  std::set<int> pressed_keys_;
 
   DISALLOW_COPY_AND_ASSIGN(UserInputMonitor);
 };