Adds the UserInputMonitor implementation for Windows.

media/media.gyp

Index: media/media.gyp
diff --git a/media/media.gyp b/media/media.gyp
index 39c75331915b4b5bf5fac00f61e6a16d6375dc0b..089c9a6dc7ed7bb15ffe7ec398d5a3ea1ea35f29 100644
--- a/media/media.gyp
+++ b/media/media.gyp
@@ -689,8 +689,6 @@
             'audio/cras/cras_input.h',
             'audio/cras/cras_unified.cc',
             'audio/cras/cras_unified.h',
-            'base/keyboard_event_counter.cc',
-            'base/keyboard_event_counter.h',
           ],
         }],
         ['use_pulseaudio==1', {
@@ -885,6 +883,12 @@
             'ENABLE_EAC3_PLAYBACK',
           ],
         }],
+        ['OS!="linux" and OS!="win"', {
+          'sources!': [
+            'base/keyboard_event_counter.cc',
+            'base/keyboard_event_counter.h',
+          ],
+        }],
       ],
       'target_conditions': [
         ['OS=="ios"', {
@@ -974,6 +978,7 @@
         'base/sinc_resampler_unittest.cc',
         'base/test_data_util.cc',
         'base/test_data_util.h',
+        'base/user_input_monitor_unittest.cc',
         'base/vector_math_testing.h',
         'base/vector_math_unittest.cc',
         'base/video_frame_unittest.cc',