[CCA] Copy missing js file to output directory

Bug: None
Test: CCA can be opened normally.
Change-Id: I502afe94b9ccedcadf1f27e6f5d19adbc51842f6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2131172
Commit-Queue: Kuo Jen Wei <inker@chromium.org>
Commit-Queue: Wei Lee <wtlee@chromium.org>
Auto-Submit: Kuo Jen Wei <inker@chromium.org>
Reviewed-by: Wei Lee <wtlee@chromium.org>
Cr-Commit-Position: refs/heads/master@{#755250}

chrome/browser/resources/chromeos/camera/BUILD.gn

@@ -149,6 +149,7 @@ copy("chrome_camera_app_js_lib") {
 
 copy("chrome_camera_app_js_models") {
   sources = [
+    "src/js/models/async_writer.js",
     "src/js/models/filenamer.js",
     "src/js/models/filesystem.js",
     "src/js/models/result_saver.js",