AudioPlayer.app: Use HTML Imports to define custom elements.

AudioPlayer.app: Use HTML Imports to define custom elements.

In Polymer 1.0, defining custom elements in the main HTML document is not currently supported.
This CL is for preparing upgrade to 1.0.

BUG=492939
TEST=manually

Committed: https://crrev.com/9123eef92f22dd054fae62234d513916f3e54d49
Cr-Commit-Position: refs/heads/master@{#333236}

[fukino, 2015-06-04 09:15:38]

fukino@chromium.org changed reviewers:
+ yoshiki@chromium.org

[fukino, 2015-06-04 09:15:39]

yoshiki@, could you take a look?
Sorry for sending many CLs... Thanks for reviews!

[yoshiki, 2015-06-08 02:19:51]

lgtm

[fukino, 2015-06-08 02:21:59]

The CQ bit was checked by fukino@chromium.org

[commit-bot: I haz the power, 2015-06-08 02:22:03]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1164983003/1

[commit-bot: I haz the power, 2015-06-08 03:20:50]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-06-08 03:21:46]

Patchset 1 (id:??) landed as
https://crrev.com/9123eef92f22dd054fae62234d513916f3e54d49
Cr-Commit-Position: refs/heads/master@{#333236}