Fix CCA create black video thumbnail bug

Bug: 936589
Test: The thumbnail can be created and shown correctly under all capture
modes.

(cherry picked from commit 67fa9ba68c0d514b156956a58b10413513dce6d4)

Change-Id: I5cd963d60bc7f03916a945a41e3e33ba05def660
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1657514
Reviewed-by: Sheng-hao Tsao <shenghao@chromium.org>
Commit-Queue: Kuo Jen Wei <inker@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#668715}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1662107
Reviewed-by: Kuo Jen Wei <inker@chromium.org>
Cr-Commit-Position: refs/branch-heads/3809@{#339}
Cr-Branched-From: d82dec1a818f378c464ba307ddd9c92133eac355-refs/heads/master@{#665002}

diff --git a/chrome/browser/resources/chromeos/camera/src/js/models/filesystem.js b/chrome/browser/resources/chromeos/camera/src/js/models/filesystem.js
index ee5c97e7..6540ed4f 100644
--- a/chrome/browser/resources/chromeos/camera/src/js/models/filesystem.js
+++ b/chrome/browser/resources/chromeos/camera/src/js/models/filesystem.js

@@ -294,6 +294,9 @@
 cca.models.FileSystem.createThumbnail_ = function(isVideo, url) {
   const thumbnailWidth = 480;
   var element = document.createElement(isVideo ? 'video' : 'img');
+  if (isVideo) {
+    element.preload = 'auto';
+  }
   return new Promise((resolve, reject) => {
     element.addEventListener(isVideo ? 'canplay' : 'load', resolve);
     element.addEventListener('error', reject);