ChromeOS OOBE: switch from iron-dropdown to <select>.

ui/webui/resources/webui_resources.grd

 <?xml version="1.0" encoding="UTF-8"?>
 <!-- This comment is only here because changes to resources are not picked up
 without changes to the corresponding grd file. -->
 <grit latest_public_release="0" current_release="1" output_all_resource_defines="false">
   <outputs>
     <output filename="grit/webui_resources.h" type="rc_header">
       <emit emit_type='prepend'></emit>
     </output>
     <output filename="grit/webui_resources_map.cc"
             type="resource_file_map_source" />
@@ skipping 296 matching lines @@
       <structure name="IDR_WEBUI_HTML_CR_UI_OVERLAY"
                  file="html/cr/ui/overlay.html" type="chrome_html" />
       <structure name="IDR_WEBUI_HTML_CR_UI_POSITION_UTIL"
                  file="html/cr/ui/position_util.html" type="chrome_html" />
       <structure name="IDR_WEBUI_HTML_EVENT_TRACKER"
                  file="html/event_tracker.html" type="chrome_html" />
       <structure name="IDR_WEBUI_HTML_ICON"
                  file="html/icon.html" type="chrome_html" />
       <structure name="IDR_WEBUI_HTML_I18N_TEMPLATE"
                  file="html/i18n_template.html" type="chrome_html" />
+      <structure name="IDR_WEBUI_HTML_MD_SELECT_CSS_HTML"
+                 file="html/md_select_css.html" type="chrome_html"
+                 flattenhtml="true" />
       <structure name="IDR_WEBUI_HTML_LOAD_TIME_DATA"
                  file="html/load_time_data.html" type="chrome_html" />
       <structure name="IDR_WEBUI_HTML_PARSE_HTML_SUBSET"
                  file="html/parse_html_subset.html" type="chrome_html" />
       <structure name="IDR_WEBUI_HTML_POLYMER"
                  file="html/polymer.html" type="chrome_html" />
       <structure name="IDR_WEBUI_HTML_I18N_BEHAVIOR"
                  file="html/i18n_behavior.html" type="chrome_html" />
       <structure name="IDR_WEBUI_HTML_UTIL"
                  file="html/util.html" type="chrome_html" />
@@ skipping 143 matching lines @@
                    file="js/chromeos/ui_account_tweaks.js"
                    type="chrome_html" />
       </if>
       <if expr="not is_android">
         <part file="cr_elements_resources.grdp" />
         <part file="polymer_resources.grdp" />
       </if>
     </structures>
   </release>
 </grit>