Make the repeat button accessible by keyboard.

ui/file_manager/audio_player/elements/repeat_button.css

Index: ui/file_manager/audio_player/elements/repeat_button.css
diff --git a/ui/file_manager/audio_player/elements/repeat_button.css b/ui/file_manager/audio_player/elements/repeat_button.css
index 7003cffacae2cd0edecabfdbab3fbc61276e7d77..5325107e779e76f1ae887a2c67ee55a991ac1e0c 100644
--- a/ui/file_manager/audio_player/elements/repeat_button.css
+++ b/ui/file_manager/audio_player/elements/repeat_button.css
@@ -2,35 +2,14 @@
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file. */
 
-:host {
-  border-radius: 2px;
-  cursor: pointer;
-  display: inline-block;
-  height: 32px;
-  outline: none;
-  position: relative;
-  width: 32px;
-}
-
-.repeat-all, .no-repeat {
+[repeat-mode=repeat-all], [repeat-mode=no-repeat] {

[fukino, 2016/11/10 09:28:32]

files-icon-button {
}
will work.

   background-image: -webkit-image-set(
       url(../assets/100/player_button_repeat.png) 1x,
       url(../assets/200/player_button_repeat.png) 2x);
 }
 
-.repeat-one {
+[repeat-mode=repeat-one] {

[fukino, 2016/11/10 09:28:32]

:host[repeat-mode='repeat-one'] files-icon-button {
}
will work.

   background-image: -webkit-image-set(
       url(../assets/100/player_button_repeat_one.png) 1x,
       url(../assets/200/player_button_repeat_one.png) 2x);
 }
-
-files-toggle-ripple {
-  background-position: center;
-  background-repeat: no-repeat;
-  height: 28px;
-  left: 2px;
-  pointer-events: none;
-  position: absolute;
-  top: 2px;
-  width: 28px;
-}