MD History: Hide sign in guide in guest mode

chrome/browser/resources/md_history/synced_device_manager.html

 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-list/iron-list.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-button/paper-button.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-item/paper-item.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-menu/paper-menu.html">
 <link rel="import" href="chrome://resources/html/cr/ui/position_util.html">
 <link rel="import" href="chrome://history/shared_style.html">
 <link rel="import" href="chrome://history/synced_device_card.html">
 
 <dom-module id="history-synced-device-manager">
@@ skipping 55 matching lines @@
       <template is="dom-repeat" items="[[syncedDevices_]]" as="syncedDevice">
         <history-synced-device-card device="[[syncedDevice.device]]"
             last-update-time="[[syncedDevice.lastUpdateTime]]"
             tabs="[[syncedDevice.tabs]]"
             separator-indexes="[[syncedDevice.separatorIndexes]]"
             search-term="[[searchTerm]]">
         </history-synced-device-card>
       </template>
     </div>
     <div id="no-synced-tabs" class="centered-message"
       hidden="[[!showNoSyncedMessage(signInState_, syncedDevices_.length)]]">

[tsergeant, 2016/07/21 08:02:43]

You should probably add guestSession here so that the value will update when
guestSession changes:

[[!showNoSyncedMessage(signInState_, syncedDevices_.length, guestSession)]]

[lshang, 2016/07/21 09:58:18]

Done.

       [[noSyncedTabsMessage(fetchingSyncedTabs_)]]
     </div>
-    <div id="sign-in-guide" hidden$="[[signInState_]]">
+    <div id="sign-in-guide" hidden$="[[!showSignInGuide(signInState_)]]">

[tsergeant, 2016/07/21 08:02:43]

And here:

[[showSignInGuide(guestSession_, signInState_)]]

[lshang, 2016/07/21 09:58:18]

Done.

       <div id="illustration"></div>
       <div id="sign-in-promo">$i18n{signInPromo}</div>
       <div id="sign-in-promo-desc">$i18n{signInPromoDesc}</div>
       <paper-button id="sign-in-button" on-tap="onSignInTap_">
         $i18n{signInButton}
       </paper-button>
     </div>
   </template>
   <script src="chrome://history/synced_device_manager.js"></script>
 </dom-module>