Add type annotations to metadata_dispatcher.js.

ui/file_manager/file_manager/foreground/js/metadata/metadata_parser.js

Index: ui/file_manager/file_manager/foreground/js/metadata/metadata_parser.js
diff --git a/ui/file_manager/file_manager/foreground/js/metadata/metadata_parser.js b/ui/file_manager/file_manager/foreground/js/metadata/metadata_parser.js
index adc0ea7e8414bb9bb475992f491866314ae165f0..05df1b38f1d0ef56e89450655f98e1c0ef00e4b8 100644
--- a/ui/file_manager/file_manager/foreground/js/metadata/metadata_parser.js
+++ b/ui/file_manager/file_manager/foreground/js/metadata/metadata_parser.js
@@ -51,6 +51,26 @@ MetadataParser.prototype.createDefaultMetadata = function() {
   };
 };
 
+/**
+ * Utility function to read specified range of bytes from file
+ * @param {File} file The file to read.
+ * @param {number} begin Starting byte(included).
+ * @param {number} end Last byte(excluded).
+ * @param {function(File, ByteReader)} callback Callback to invoke.
+ * @param {function(string)} onError Error handler.
+ */
+MetadataParser.readFileBytes = function(file, begin, end, callback, onError) {
+  var fileReader = new FileReader();
+  fileReader.onerror = function(event) {
+    onError(event.type);
+  };
+  fileReader.onloadend = function() {
+    callback(file, new ByteReader(
+        /** @type {ArrayBuffer} */ (fileReader.result)));
+  };
+  fileReader.readAsArrayBuffer(file.slice(begin, end));
+};
+
 /* Base class for image metadata parsers */
 function ImageParser(parent, type, urlFilter) {
   MetadataParser.apply(this, arguments);