Files SWA: Change main.js to load the SWA fakes

Change SWA main.js to wait for the fakes to load before loading the
Files app legacy UI.

Bug: 1113981
Change-Id: I56da89ee49b4512066e2533b967da99cfb758032
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2586498
Commit-Queue: Luciano Pacheco <lucmult@chromium.org>
Auto-Submit: Luciano Pacheco <lucmult@chromium.org>
Reviewed-by: Noel Gordon <noel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#836012}

chromeos/components/file_manager/resources/main.js

@@ -5,22 +5,48 @@
 import {BrowserProxy} from './browser_proxy.js'
 import {ScriptLoader} from './script_loader.js'
 
+/**
+ * @const {boolean}
+ */
+window.isSWA = true;
+
 /**
  * Represents file manager application. Starting point for the application
  * interaction.
  */
 class FileManagerApp {
   constructor() {
-    console.info('File manager app created ...');
+    /**
+     * Creates a Mojo pipe to the C++ SWA container.
+     * @private @const {!BrowserProxy}
+     */
+    this.browserProxy_ = new BrowserProxy();
   }
 
+  /** @return {!BrowserProxy} */
+  get browserProxy() {
+    return this.browserProxy_;
+  }
+
+  /**
+   * Start-up: load the page scripts in order: fakes first (to provide chrome.*
+   * API that the files app foreground scripts expect for initial render), then
+   * the files app foreground scripts. Note main_scripts.js should have 'defer'
+   * true per crbug.com/496525.
+   */
   async run() {
-    await new ScriptLoader('legacy_main_scripts.js').load();
-    console.debug('Legacy code loaded');
+    await Promise.all([
+        new ScriptLoader('file_manager_private_fakes.js').load(),
+        new ScriptLoader('file_manager_fakes.js').load(),
+    ]);
+
+    await Promise.all([
+      new ScriptLoader('foreground/js/elements_importer.js').load(),
+      new ScriptLoader('foreground/js/main_scripts.js', {defer: true}).load(),
+    ]);
+    console.debug('Files app legacy UI loaded');
   }
 }
 
 const app = new FileManagerApp();
-document.addEventListener('DOMContentLoaded', () => {
-  app.run();
-});
+app.run();