Files app: Fix race when initializing as JS modules

The i18n strings in the deferred elements need the `loadTimeData` which
is initialized in the background page and in the
initBackgroundPagePromise_.  Change the initialization for JS modules to
wait the background promise before importing the deferred elements.

Bug: 1133186
Change-Id: I2f82cc3ca89964900c5711652379fbcbdff17acb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2641785
Commit-Queue: Jeremie Boulic <jboulic@chromium.org>
Reviewed-by: Jeremie Boulic <jboulic@chromium.org>
Cr-Commit-Position: refs/heads/master@{#845544}

ui/file_manager/file_manager/foreground/js/BUILD.gn

@@ -2142,7 +2142,6 @@ js_modulizer("modulize") {
                          "cr.ui.MultiMenu|MultiMenu",
                          "cr.ui.ComboButton|ComboButton",
                          "cr.filebrowser.DefaultTaskDialog|DefaultTaskDialog",
-                         "window.importElementsPromise|importElements",
                        ]
 }
 

ui/file_manager/file_manager/foreground/js/elements_importer.m.js

@@ -24,3 +24,6 @@ export function importElements() {
     document.head.appendChild(script);
   });
 }
+
+// TODO: Remove this initialization once non-JS module is removed.
+window.importElements = importElements;

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

@@ -874,8 +874,16 @@
     this.document_ = this.dialogDom_.ownerDocument;
 
     metrics.startInterval('Load.InitDocuments');
-    await Promise.all(
-        [this.initBackgroundPagePromise_, window.importElementsPromise]);
+    if (window.importElementsPromise) {
+      // For non-js modules version these promises can run in parallel.
+      await Promise.all(
+          [this.initBackgroundPagePromise_, window.importElementsPromise]);
+    } else if (window.importElements) {
+      // importElements depend on loadTimeData which is initialized in the
+      // initBackgroundPagePromise_.
+      await this.initBackgroundPagePromise_;
+      await window.importElements();
+    }
     metrics.recordInterval('Load.InitDocuments');
 
     metrics.startInterval('Load.InitUI');