Files app: Fix integration tests that uses getLastVisitedURL()

When running Files app as JS modules the util namespace isn't accessible
to test_util.js.  Expose the only required function via the `fileManager`
instance which is accessible to test_util.js

Bug: 1133186
Change-Id: I1b2fe3f702b1f62e954250496818c808fd72aa6b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2639440
Commit-Queue: Luciano Pacheco <lucmult@chromium.org>
Commit-Queue: Jeremie Boulic <jboulic@chromium.org>
Auto-Submit: Luciano Pacheco <lucmult@chromium.org>
Reviewed-by: Jeremie Boulic <jboulic@chromium.org>
Cr-Commit-Position: refs/heads/master@{#845080}

ui/file_manager/file_manager/background/js/test_util.js

@@ -289,7 +289,7 @@ test.util.sync.getTreeItems = contentWindow => {
  * @return {!string} The URL of the last URL visited.
  */
 test.util.sync.getLastVisitedURL = contentWindow => {
-  return contentWindow.util.getLastVisitedURL();
+  return contentWindow.fileManager.getLastVisitedURL();
 };
 
 /**

ui/file_manager/file_manager/foreground/js/file_manager.js

@@ -588,6 +588,15 @@
     this.fileBrowserBackground_.launchFileManager(appState);
   }
 
+  /**
+   * Returns the last URL visited with visitURL() (e.g. for "Manage in Drive").
+   * Used by the integration tests.
+   * @return {string}
+   */
+  getLastVisitedURL() {
+    return util.getLastVisitedURL();
+  }
+
   /**
    * One time initialization for app state controller to load view option from
    * local storage.