[Files.app] Minor fix of the annotation in content_metadata_provider.js

BUG=448263
TEST=none

Review URL: https://codereview.chromium.org/1008003005

Cr-Commit-Position: refs/heads/master@{#320898}

ui/file_manager/file_manager/foreground/js/metadata/content_metadata_provider.js

@@ -167,7 +167,7 @@ ContentMetadataProvider.prototype.onMessage_ = function(event) {
 
 /**
  * Handles the 'initialized' message from the metadata reader Worker.
- * @param {Object} regexp Regexp of supported urls.
+ * @param {RegExp} regexp Regexp of supported urls.
  * @private
  */
 ContentMetadataProvider.prototype.onInitialized_ = function(regexp) {