Use strict and expose in build version

src/metadata.js

@@ -1,4 +1,6 @@
-var Metadata = (function MetadataClosure() {
+'use strict';
+
+var Metadata = PDFJS.Metadata = (function MetadataClosure() {
   function Metadata(meta) {
     if (typeof meta === 'string') {
       var parser = new DOMParser();

web/viewer.js

@@ -506,7 +506,7 @@ var PDFView = {
     var pdfTitle;
 
     if (metadata) {
-      this.metadata = metadata = new Metadata(metadata);
+      this.metadata = metadata = new PDFJS.Metadata(metadata);
 
       if (metadata.has('dc:title'))
         pdfTitle = metadata.get('dc:title');