PDFs viewed inside a <webview> should navigate the same as PDFs in tabs.

chrome/browser/resources/pdf/navigator.js

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 'use strict';
 
 /**
  * Creates a new Navigator for navigating to links inside or outside the PDF.
+ * @param {int} tabId of browser tab containing viewer, -1 if in <webview>
  * @param {string} originalUrl The original page URL.
  * @param {Object} viewport The viewport info of the page.
  * @param {Object} paramsParser The object for URL parsing.
  * @param {Function} navigateInCurrentTabCallback The Callback function that
  *    gets called when navigation happens in the current tab.
  * @param {Function} navigateInNewTabCallback The Callback function that gets
  *    called when navigation happens in the new tab.
  */
-function Navigator(originalUrl,
+function Navigator(tabId,
+                   originalUrl,
                    viewport,
                    paramsParser,
                    navigateInCurrentTabCallback,
                    navigateInNewTabCallback) {
+  this.tabId_ = tabId;
   this.originalUrl_ = originalUrl;
   this.viewport_ = viewport;
   this.paramsParser_ = paramsParser;
   this.navigateInCurrentTabCallback_ = navigateInCurrentTabCallback;
   this.navigateInNewTabCallback_ = navigateInNewTabCallback;
 }
 
 Navigator.prototype = {
   /**
    * @private
@@ skipping 126 matching lines @@
     if (isRelative) {
       var slashIndex = this.originalUrl_.lastIndexOf('/');
       var path = slashIndex != -1 ?
           this.originalUrl_.substr(0, slashIndex) : this.originalUrl_;
       return path + '/' + url;
     }
 
     return 'http://' + url;
   }
 };