PDF: Use PDF metadata for the title instead of the last path element.

chrome/browser/resources/pdf/elements/viewer-pdf-toolbar/viewer-pdf-toolbar.html

 <link rel="import" href="chrome://resources/polymer/v1_0/polymer/polymer.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-flex-layout/classes/iron-shadow-flex-layout.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-icons/image-icons.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-icons/iron-icons.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/neon-animation/animations/slide-down-animation.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/neon-animation/animations/slide-up-animation.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/neon-animation/neon-animation-runner-behavior.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-icon-button/paper-icon-button.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-material/paper-material.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-progress/paper-progress.html">
@@ skipping 17 matching lines @@
 
         <div class="flex-1" id="pageselector-container">
           <viewer-page-selector id="pageselector" class="invisible"
               doc-length="{{docLength}}" page-no="{{pageNo}}">
           </viewer-page-selector>
         </div>
 
         <div id="buttons" class="invisible flex-5">
           <!-- TODO(tsergeant): "Bookmarks" should be localized. -->
           <viewer-toolbar-dropdown id="bookmarks"
-                                   hidden$="[[!bookmarks]]"
+                                   hidden$="[[!bookmarks.length]]"
                                    header="Bookmarks"
                                    open-icon="bookmark"
                                    closed-icon="bookmark-border">
               <viewer-bookmarks-content bookmarks="{{bookmarks}}">
               </viewer-bookmarks-content>
           </viewer-toolbar-dropdown>
           <paper-icon-button icon="image:rotate-right"
               on-click="rotateRight"></paper-icon-button>
           <!-- TODO(tsergeant): Replace this placeholder with a more useful
                 button. -->
           <paper-icon-button icon="image:rotate-left"
               on-click="rotateLeft"></paper-icon-button>
           <paper-icon-button icon="save"
               on-click="save"></paper-icon-button>
           <paper-icon-button icon="print"
               on-click="print"></paper-icon-button>
         </div>
       </div>
     </paper-toolbar>
   </template>
 </dom-module>
 <script src="viewer-pdf-toolbar.js"></script>