CCA: Fix error handling for thumbnail generation

In the old code an Event would be rejected instead of an Error. This CL
fixes that with a better error message for video.

Bug: 1140852
Test: Load an invalid video manually.
Change-Id: Ia659eddff5d8406c44d61fa1a6f556e61ddf2b7a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2509613
Auto-Submit: Shik Chen <shik@chromium.org>
Reviewed-by: Wei Lee <wtlee@chromium.org>
Commit-Queue: Wei Lee <wtlee@chromium.org>
Cr-Commit-Position: refs/heads/master@{#822603}

chromeos/components/camera_app_ui/resources/js/util.js

@@ -369,7 +369,22 @@ export async function scalePicture(url, isVideo, width, height = undefined) {
   }
   await new Promise((resolve, reject) => {
     element.addEventListener(isVideo ? 'canplay' : 'load', resolve);
-    element.addEventListener('error', reject);
+    element.addEventListener('error', () => {
+      if (isVideo) {
+        let msg = 'Failed to load video';
+        /**
+         * https://developer.mozilla.org/en-US/docs/Web/API/HTMLMediaElement/error
+         * @type {?MediaError}
+         */
+        const err = element.error;
+        if (err !== null) {
+          msg += `: ${err.message}`;
+        }
+        reject(new Error(msg));
+      } else {
+        reject(new Error('Failed to load image'));
+      }
+    });
     element.src = url;
   });
   if (height === undefined) {