Adds the UserInputMonitor implementation for Windows.

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
index c82ca597eef11240a9b7a73d665ab9d24a6ba8c8..d8e76b0d850a84b5be524bc677692610f0d25a3b 100644
--- a/media/base/keyboard_event_counter.h
+++ b/media/base/keyboard_event_counter.h
@@ -8,6 +8,7 @@
 #include <set>
 
 #include "base/synchronization/lock.h"
+#include "media/base/media_export.h"
 #include "ui/base/events/event_constants.h"
 #include "ui/base/keycodes/keyboard_codes.h"
 
@@ -17,7 +18,7 @@ namespace media {
 // 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.
-class KeyboardEventCounter {
+class MEDIA_EXPORT KeyboardEventCounter {
  public:
   KeyboardEventCounter();
   ~KeyboardEventCounter();