[quickview] Add CommandHandler.getCommand(name)

Add a public CommandHandler method to get a handler by name. Not used
yet but required for Quick View to get hold of the delete handler.

Bug: 803259
Change-Id: Iddca1284363d40de64629458b28a6d646636d859
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2026331Reviewed-by: Noel Gordon <noel@chromium.org>
Commit-Queue: Noel Gordon <noel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#736253}

ui/file_manager/file_manager/foreground/js/file_manager_commands.js

@@ -451,6 +451,15 @@ class CommandHandler {
     handler.canExecute.call(
         /** @type {Command} */ (handler), event, this.fileManager_);
   }
+
+  /**
+   * Returns command handler by name.
+   * @param {string} name The command name.
+   * @public
+   */
+  static getCommand(name) {
+    return CommandHandler.COMMANDS_[name];
+  }
 }
 
 /**