Add custom Polymer network icon element

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">
   <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 184 matching lines @@
       <include name="IDR_WEBUI_IMAGES_SELECT"
                file="images/select.png" type="BINDATA" />
       <include name="IDR_WEBUI_IMAGES_SPINNER"
                file="images/spinner.svg" type="BINDATA" />
       <include name="IDR_WEBUI_IMAGES_THROBBER"
                file="images/throbber.svg" type="BINDATA" />
       <include name="IDR_WEBUI_IMAGES_TRASH"
                file="images/trash.png" type="BINDATA" />
       <include name="IDR_WEBUI_IMAGES_CLOUDS"
                file="images/clouds.png" type="BINDATA" />
+
+      <part file="cr_elements_images.grdp" />
     </includes>
     <structures>
       <structure name="IDR_WEBUI_CSS_ALERT_OVERLAY"
                  file="css/alert_overlay.css" type="chrome_html" />
       <structure name="IDR_WEBUI_CSS_BUBBLE"
                  file="css/bubble.css" type="chrome_html" />
       <structure name="IDR_WEBUI_CSS_BUBBLE_BUTTON"
                  file="css/bubble_button.css" type="chrome_html" />
       <structure name="IDR_WEBUI_CSS_BUTTER_BAR"
                  file="css/butter_bar.css" type="chrome_html" />
@@ skipping 169 matching lines @@
                    type="chrome_html" />
         <structure name="IDR_WEBUI_JS_UI_ACCOUNT_TWEAKS"
                    file="js/chromeos/ui_account_tweaks.js"
                    type="chrome_html" />
       </if>
       <part file="cr_elements_resources.grdp" />
       <part file="polymer_resources.grdp" />
     </structures>
   </release>
 </grit>