config_service: make UI adjustable for mobile

appengine/config_service/ui/common/auth-signin.html

 <!--
   Copyright 2017 The LUCI Authors. All rights reserved.
   Use of this source code is governed under the Apache License, Version 2.0
   that can be found in the LICENSE file.
 
   The `auth-signin` element displays sign-in/sign-out button, user email and
   avatar.
   It has a google-signin/google-signin-aware element under the hood that handles
   the actual OAuth logic.
 
@@ skipping 37 matching lines @@
       client-id="[[client_id]]"
       initialized="{{initialized}}"
       scopes="email"
       on-google-signin-aware-success="_onSignin"
       on-google-signin-aware-signed-out="_onSignout">
     </google-signin-aware>
 
     <template is="dom-if" if="[[!signed_in]]">
       <div id="signinContainer">
         <!-- TODO(cwpayton): Before official deployment, change href to "/#/" -->
-        <a class="typeface" on-tap="signIn" href="/#/">Sign in</a>
+        <a class="typeface" on-tap="signIn" href="[[current_url]]">Sign in</a>
       </div>
     </template>
 
     <template is="dom-if" if="[[signed_in]]">
       <img class="center" id="avatar" src="[[profile.imageUrl]]" width="30" height="30">
       <span class="center typeface">[[profile.email]]</span>
       <span class="center typeface">|</span>
       <!-- TODO(cwpayton): Before official deployment, change href to "/#/" -->
       <a class="center typeface" on-tap="signOut" href="/#/">Sign out</a>
     </template>
@@ skipping 12 matching lines @@
         auth_response: {
           type: Object,
           notify: true,
           observer: '_makeHeader'
         },
 
         client_id: {
           type: String
         },
 
+        current_url: {
+          type: String,
+          value: "/#/"
+        },
+
         initialized: {
           type: Boolean,
           value: false,
           observer: '_onInitialized'
         },
 
         profile: {
           type: Object,
           notify: true
         },
@@ skipping 57 matching lines @@
           this.set('auth_headers', null);
         }
         this.set('auth_headers', 
             {
               "authorization": this.auth_response.token_type + " " +
                                this.auth_response.access_token
             });
       },
 
       signIn: function() {
+        this.current_url = window.location.href;
         this.$.aware.signIn();
       },
 
       signOut: function() {
         this.$.aware.signOut();
         window.location.reload();
       }
     });
   </script>
 </dom-module>