Added a message that suggest to configure a proxy for a network.

chrome/browser/resources/chromeos/login/screen_error_message.html

 <div id="error-message" class="step faded hidden show-offline-message">
   <div id="error-message-screen-title">
     <span id="error-message-title" i18n-content="offlineMessageTitle"
         class="show-with-offline-message"></span>
     <span id="captive-portal-title" i18n-content="captivePortalTitle"
         class="show-with-captive-portal show-with-proxy-error"></span>
   </div>
   <div id="error-message-body">
     <span id="offline-message-text" i18n-content="offlineMessageBody"
         class="show-with-offline-message"></span>
     <div id="captive-portal-message-text"
         class="show-with-captive-portal"></div>
+    <div id="captive-portal-proxy-message-text"
+        class="show-with-captive-portal"></div>
     <div id="proxy-message-text"
         class="show-with-proxy-error"></div>
-    <div id="captive-portal-network-select-text"
-        class="show-with-captive-portal">
-      <span i18n-content="captivePortalNetworkSelect"></span>
-    </div>
   </div>
   <div id="offline-network-control" class="control-with-label">
     <label for="offline-networks-list-dropdown" i18n-content="selectNetwork"
-        class="label menu-control"></label>
+        class="flexible-label dont-show-with-captive-portal"></label>
+    <label for="offline-networks-list-dropdown"
+        i18n-content="selectAnotherNetwork"
+        class="flexible-label show-with-captive-portal"></label>
     <div class="menu-area">
       <div id="offline-networks-list" class="menu-control">
       </div>
     </div>
   </div>
   <div id="error-guest-signin"
       class="show-with-offline-message show-with-captive-portal"></div>
   <div id="error-offline-login"
       class="show-with-offline-message show-with-captive-portal"></div>
 </div>