remove loadCallback in favor of the pdf-loaded event

pdf.js

@@ -265,17 +265,6 @@ function PDFViewer(browserApi) {
 }
 
 PDFViewer.prototype = {
-  /**
-   * Sets the callback which will be run when the PDF document has finished
-   * loading. If the document is already loaded, it will be run immediately.
-   * @param {Function} callback the callback to be called.
-   */
-  setLoadCallback: function(callback) {
-    this.loadCallback_ = callback;
-    if (this.loadState_ != LoadState.LOADING && this.loadCallback_)
-      this.loadCallback_(this.loadState_ == LoadState.SUCCESS);
-  },
-
   /**
    * @private
    * Handle key events. These may come from the user directly or via the
@@ -516,9 +505,7 @@ PDFViewer.prototype = {
   sendDocumentLoadedMessage_: function() {
     if (this.loadState_ == LoadState.LOADING)
       return;
-    if (this.loadCallback_)
-      this.loadCallback_(this.loadState_ == LoadState.SUCCESS);
-    window.dispatchEvent(new Event('pdf-loaded'))
+    window.dispatchEvent(new Event('pdf-loaded', this.loadState_))
     this.sendScriptingMessage_({
       type: 'documentLoaded',
       load_state: this.loadState_