[M90] Files SWA: Simplify loadTimeData loading

We special cased loadTimeData for SWA File Manager in the background
code. This had the side effect of including 'strings.js' twice in the
elements at run time.

Remove the special casing in the background code.

(cherry picked from commit 95badd6)

Bug: 1113981
Change-Id: I5777dbbd8107c52cd880d1d8ad663d46dccf2d97
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2719784
Reviewed-by: Bo Majewski <majewski@chromium.org>
Commit-Queue: Alex Danilo <adanilo@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#858040}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2737875
Auto-Submit: Alex Danilo <adanilo@chromium.org>
Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/branch-heads/4430@{#144}
Cr-Branched-From: e5ce7dc-refs/heads/master@{#857950}

ui/file_manager/file_manager/background/js/background_base.js

@@ -24,30 +24,16 @@
     this.dialogs = {};
 
     // Initializes the strings. This needs for the volume manager.
-    if (!window.isSWA) {
-      this.initializationPromise_ = new Promise((fulfill, reject) => {
-        chrome.fileManagerPrivate.getStrings(stringData => {
-          if (chrome.runtime.lastError) {
-            console.error(chrome.runtime.lastError.message);
-            return;
-          }
-          loadTimeData.data = assert(stringData);
-          fulfill(stringData);
-        });
-      });
-    } else {
-      this.initializationPromise_ = new Promise((fulfill, reject) => {
-        const script = document.createElement('script');
-
-        script.onload = () => {
-          // window.loadTimeData.data_ = null; // Gambiarra!
-          fulfill(window.loadTimeData.data_);
-        };
-
-        document.head.append(script);
-        script.src = 'strings.js';
+    this.initializationPromise_ = new Promise((fulfill, reject) => {
+      chrome.fileManagerPrivate.getStrings(stringData => {
+        if (chrome.runtime.lastError) {
+          console.error(chrome.runtime.lastError.message);
+          return;
+        }
+        loadTimeData.data = assert(stringData);
+        fulfill(stringData);
       });
-    }
+    });
 
     /** @private {?LaunchHandler} */
     this.launchHandler_ = null;