Remove addPageLoadHandler use from file manager main.js

Call DOMContentLoaded directly. Update comments.

Bug: 887792
Change-Id: Ib688e8dda1b74ff065e91a980099050ca19cb8a4
Reviewed-on: https://chromium-review.googlesource.com/1237018Reviewed-by: Luciano Pacheco <lucmult@chromium.org>
Reviewed-by: Trent Apted <tapted@chromium.org>
Commit-Queue: Noel Gordon <noel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#593068}

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

@@ -9,16 +9,17 @@ var fileManager;
 
 /**
  * Indicates if the DOM and scripts have been already loaded.
+ * TODO(noel): is this variable used anywhere?
  * @type {boolean}
  */
 var pageLoaded = false;
 
 /**
- * Kick off the file manager dialog.
- * Called by main.html after the DOM has been parsed.
+ * Initializes the File Manager UI and starts the File Manager dialog. Called
+ * by main.html after the DOM and all scripts have been loaded.
+ * @param event DOMContentLoaded event.
  */
-function init() {
-  // Initializes UI and starts the File Manager dialog.
+function init(event) {
   fileManager.initializeUI(document.body).then(function() {
     util.testSendMessage('ready');
     metrics.recordInterval('Load.Total');
@@ -26,15 +27,15 @@ function init() {
   });
 }
 
-// Create the File Manager object. Note, that the DOM, nor any external
-// scripts may not be ready yet.
+// Creates the File Manager object. Note that the DOM, or any external
+// scripts, may not be ready yet.
 fileManager = new FileManager();
 
-// Initialize the core stuff, which doesn't require access to DOM nor to
-// additional scripts.
+// Initialize the core stuff, which doesn't require access to the DOM or
+// to external scripts.
 fileManager.initializeCore();
 
-// Final initialization is performed after all scripts and DOM is loaded.
-util.addPageLoadHandler(init);
+// Final initialization performed after DOM and all scripts have loaded.
+document.addEventListener('DOMContentLoaded', init);
 
 metrics.recordInterval('Load.Script');  // Must be the last line.