Make the repeat button accessible by keyboard.

ui/file_manager/audio_player/elements/repeat_button.html

Index: ui/file_manager/audio_player/elements/repeat_button.html
diff --git a/ui/file_manager/audio_player/elements/repeat_button.html b/ui/file_manager/audio_player/elements/repeat_button.html
index c38390cafdf18e56b2bf049a21b1577c1e1c4a4a..5af558ebbba1f4fd33fb403911610e01a27459f3 100644
--- a/ui/file_manager/audio_player/elements/repeat_button.html
+++ b/ui/file_manager/audio_player/elements/repeat_button.html
@@ -4,12 +4,14 @@
   -->
 
 <link rel="import" href="chrome://resources/polymer/v1_0/polymer/polymer.html">
-<link rel="import" href="chrome-extension://hhaomjibdihmijegdhdafkllkbggdgoj/foreground/elements/files_toggle_ripple.html">
+<link rel="import" href="chrome-extension://hhaomjibdihmijegdhdafkllkbggdgoj/foreground/elements/files_icon_button.html">
 
 <dom-module id="repeat-button">
   <link rel="import" type="css" href="repeat_button.css">
   <template>
-    <files-toggle-ripple activated="[[isActive(repeatMode)]]" class$="{{repeatMode}}"></files-toggle-ripple>
+    <files-icon-button active="[[isActive(repeatMode)]]"
+                       repeat-mode$="{{repeatMode}}" toggles>

[fukino, 2016/11/10 08:30:19]

What is the intention to change "class$=" to "repeat-mode$="?
I guess class$= still works and we won't need to modify tests with it?

[yamaguchi, 2016/11/10 08:43:16]

To avoid that keyboard focus indicator disappears when hitting Enter key on the
button.
https://codereview.chromium.org/2482063002/#ps40001

When we put the toggle status as a part of class attribute, I found the script
will remove the "keyboard-focus" value in class attribute here:
https://cs.chromium.org/chromium/src/third_party/catapult/third_party/polymer...
which should have been added by files-icon-button:
https://cs.chromium.org/chromium/src/ui/file_manager/file_manager/foreground/...

I am not yet 100% sure if there's a better solution, though.

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

I see.
Since the repeatMode's refrectToAttribute is true, we can set background image
without this binding. I left comment in the css file.

+    </files-icon-button>
   </template>
 
   <script src="repeat_button.js"></script>