The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/53b690eb87b6c8786574622243893049d3745bde

commit 53b690eb87b6c8786574622243893049d3745bde
Author: stevenjb <stevenjb@chromium.org>
Date: Tue Jul 12 00:46:40 2016

Unify iron-dropdown CSS

Moves shared CSS for iron-dropdown to settings_shared_css.html.
Also makes dropdown items actionable.

BUG= 621731 
CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2133793003
Cr-Commit-Position: refs/heads/master@{#404756}

[modify] https://crrev.com/53b690eb87b6c8786574622243893049d3745bde/chrome/browser/resources/settings/bluetooth_page/bluetooth_device_list_item.html
[modify] https://crrev.com/53b690eb87b6c8786574622243893049d3745bde/chrome/browser/resources/settings/languages_page/languages_page.html
[modify] https://crrev.com/53b690eb87b6c8786574622243893049d3745bde/chrome/browser/resources/settings/on_startup_page/startup_url_entry.html
[modify] https://crrev.com/53b690eb87b6c8786574622243893049d3745bde/chrome/browser/resources/settings/settings_shared_css.html

Also:
* The menu is not placed correctly when near the bottom edge of the screen, instead a scrollbar is shown.
* The scrollbar overlaps the margin making the content look cramped.

Note: this is the pattern we use in md-settings for iron-dropdown:

  <iron-dropdown opened="{{menuOpened}}">
    <div class="dropdown-content">
      <paper-item id="item1" on-tap="onTap_">Item1</paper-item>
      <paper-item id="item2" on-tap="onTap_">Item2</paper-item>
    </div>
  </iron-dropdown>

We would prefer to replace <paper-item> with <div> to reduce overhead on page load.

Note: for issues with paper-dropdown-item, see  issue 624303 

All reported issues are addressed as part of https://bugs.chromium.org/p/chromium/issues/detail?id=639718, except for the in/out animation.

Fixed as part of  issue 639718 .