Make the repeat button accessible by keyboard.

ui/file_manager/audio_player/elements/repeat_button.js

Index: ui/file_manager/audio_player/elements/repeat_button.js
diff --git a/ui/file_manager/audio_player/elements/repeat_button.js b/ui/file_manager/audio_player/elements/repeat_button.js
index 51f5b9ca01654da70f5dbccf6d921958a94644f4..48e68d52aefb229640529d6bfcc177371c0a43e8 100644
--- a/ui/file_manager/audio_player/elements/repeat_button.js
+++ b/ui/file_manager/audio_player/elements/repeat_button.js
@@ -10,6 +10,16 @@
 Polymer({
   is: 'repeat-button',
 
+  hostAttributes: {
+    role: 'button',
+    tabindex: 0
+  },
+
+  behaviors: [
+    Polymer.IronButtonState,
+    Polymer.IronControlState
+  ],
+
   properties: {
     'repeatMode': {
       type: String,
@@ -22,6 +32,18 @@ Polymer({
     tap: '_tapHandler'
   },
 
+  observers: [
+    '_focusedChanged(receivedFocusFromKeyboard)'
+  ],
+
+  _focusedChanged: function(receivedFocusFromKeyboard) {
+    if (receivedFocusFromKeyboard) {
+      this.classList.add('keyboard-focus');
+    } else {
+      this.classList.remove('keyboard-focus');
+    }
+  },
+
   /**
    * Initialize member variables.
    */