Introduce new test for bookmark loading.

chrome/browser/resources/pdf/pdf.js

Index: chrome/browser/resources/pdf/pdf.js
diff --git a/chrome/browser/resources/pdf/pdf.js b/chrome/browser/resources/pdf/pdf.js
index c9b50d9d9c72eda9eee4a42f1cf9e631ee3c64a1..22062a27d1bc40760d4aa76d1f35696ecc37e84d 100644
--- a/chrome/browser/resources/pdf/pdf.js
+++ b/chrome/browser/resources/pdf/pdf.js
@@ -709,5 +709,16 @@ PDFViewer.prototype = {
    */
   get viewport() {
     return this.viewport_;
+  },
+
+  /**
+   * Each bookmark is an Object containing a:
+   * - title
+   * - page (optional)
+   * - array of children (themselves bookmarks)
+   * @type {Array} the top-level bookmarks of the PDF.
+   */
+  get bookmarks() {
+    return this.bookmarks_;
   }
 };