Remove ids from viewer page and thumbnail divs

The id, and parsing it for the page number, is replaced by the
data-page-number attribute (added here for thumbnails).

web/pdf_page_view.js

@@ -112,7 +112,6 @@ var PDFPageView = (function PDFPageViewClosure() {
     this.annotationLayer = null;
 
     var div = document.createElement('div');
-    div.id = 'pageContainer' + this.id;
     div.className = 'page';
     div.style.width = Math.floor(this.viewport.width) + 'px';
     div.style.height = Math.floor(this.viewport.height) + 'px';

web/pdf_thumbnail_view.js

@@ -124,8 +124,8 @@ var PDFThumbnailView = (function PDFThumbnailViewClosure() {
     this.anchor = anchor;
 
     var div = document.createElement('div');
-    div.id = 'thumbnailContainer' + id;
     div.className = 'thumbnail';
+    div.setAttribute('data-page-number', this.id);
     this.div = div;
 
     if (id === 1) {

web/pdf_thumbnail_viewer.js

@@ -87,7 +87,8 @@ var PDFThumbnailViewer = (function PDFThumbnailViewerClosure() {
       if (selected) {
         selected.classList.remove('selected');
       }
-      var thumbnail = document.getElementById('thumbnailContainer' + page);
+      var thumbnail = document.querySelector(
+        'div.thumbnail[data-page-number="' + page + '"]');
       if (thumbnail) {
         thumbnail.classList.add('selected');
       }