update elements and fix some bugs

lib/src/google-signin/google-signin.html

Index: lib/src/google-signin/google-signin.html
diff --git a/lib/src/google-signin/google-signin.html b/lib/src/google-signin/google-signin.html
index 5bf7f958ce969abc2797613130750ee5c3f712c3..b8496df0118aef57de4253a659843ef16a7dd7c2 100644
--- a/lib/src/google-signin/google-signin.html
+++ b/lib/src/google-signin/google-signin.html
@@ -17,6 +17,9 @@
       client-id="{{clientId}}"
       cookie-policy="{{cookiePolicy}}"
       request-visible-actions="{{requestVisibleActions}}"
+      hosted-domain="{{hostedDomain}}"
+      offline="{{offline}}"
+      offline-always-prompt="{{offlineAlwaysPrompt}}"
       scopes="{{scopes}}"
       signed-in="{{signedIn}}"
       is-authorized="{{isAuthorized}}"
@@ -144,6 +147,13 @@ activities (https://developers.google.com/+/web/app-activities/) on behalf of
 the user. Please note that this attribute is only valid in combination with the
 plus.login scope (https://www.googleapis.com/auth/plus.login).
 
+The `offline` attribute allows you to get an auth code which your server can
+redeem for an offline access token
+(https://developers.google.com/identity/sign-in/web/server-side-flow).
+You can also set `offline-always-prompt` instead of `offline` to ensure that your app
+will re-prompt the user for offline access and generate a working `refresh_token`
+even if they have already granted offline access to your app in the past.
+
 Use label properties to customize prompts.
 
 The button can be styled in using the `height`, `width`, and `theme` attributes.
@@ -151,12 +161,15 @@ These attributes help you follow the Google+ Sign-In button branding guidelines
 (https://developers.google.com/+/branding-guidelines).
 
 The `google-signin-success` event is triggered when a user successfully authenticates
-and `google-signed-out` is triggered when user signeds out.
+and `google-signed-out` is triggered when user signs out.
 You can also use `isAuthorized` attribute to observe user's authentication state.
 
 Additional events, such as `google-signout-attempted` are
 triggered when the user attempts to sign-out and successfully signs out.
 
+When requesting offline access, the `google-signin-offline-success` event is
+triggered when the user successfully consents with offline support.
+
 The `google-signin-necessary` event is fired when scopes requested via
 google-signin-aware elements require additional user permissions.
 
@@ -197,6 +210,14 @@ any apps you're building. See the Google Developers Console
      */
 
     /**
+     * Fired when an offline authorization is successful.
+     * @event google-signin-offline-success
+     * @param {Object} detail
+     * @param {string} detail.code The one-time authorization code from Google.
+     *     Your application can exchange this for an `access_token` and `refresh_token`
+     */
+
+    /**
      * Fired when this scope is not authorized
      * @event google-signin-aware-signed-out
      */
@@ -287,6 +308,7 @@ any apps you're building. See the Google Developers Console
           type: String,
           computed: '_computeSigninLabel(labelSignin, width, _brand)'
         },
+
         /**
          * An optional label for the sign-out button.
          */
@@ -313,6 +335,33 @@ any apps you're building. See the Google Developers Console
         },
 
         /**
+         * The Google Apps domain to which users must belong to sign in.
+         * See the relevant [docs](https://developers.google.com/identity/sign-in/web/reference) for more information.
+         */
+        hostedDomain: {
+          type: String,
+          value: ''
+        },
+
+        /**
+         * Allows for offline `access_token` retrieval during the signin process.
+         */
+        offline: {
+          type: Boolean,
+          value: false
+        },
+
+        /**
+         * Forces a re-prompt, even if the user has already granted offline
+         * access to your application in the past. You only need one of
+         * `offline` and `offlineAlwaysPrompt`.
+         */
+        offlineAlwaysPrompt: {
+          type: Boolean,
+          value: false
+        },
+
+        /**
          * The scopes to provide access to (e.g https://www.googleapis.com/auth/drive)
          * and should be space-delimited.
          */