Downloads WebUI: change toast duration to 10s

Bug: 949508
Change-Id: I59edf4066c7090598cf1bf9a723a6ec955c46f2b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1597640Reviewed-by: Hector Carmona <hcarmona@chromium.org>
Commit-Queue: Esmael El-Moslimany <aee@chromium.org>
Cr-Commit-Position: refs/heads/master@{#657343}

chrome/browser/resources/downloads/manager.html

@@ -142,7 +142,8 @@
       </div>
     </div>
     <cr-toast-manager on-undo-click="onUndoClick_" undo-label="$i18n{undo}"
-        undo-description="$i18n{undoDescription}"></cr-toast-manager>
+        undo-description="$i18n{undoDescription}" duration="10000">
+    </cr-toast-manager>
   </template>
   <script src="chrome://downloads/manager.js"></script>
 </dom-module>