Make the scripting OOP PDF API easier to use (take 2)

chrome/browser/resources/pdf/pdf_scripting_api.js

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 /**
  * Create a new PDFScriptingAPI. This provides a scripting interface to
  * the PDF viewer so that it can be customized by things like print preview.
  * @param {Window} window the window of the page containing the pdf viewer.
  * @param {Object} plugin the plugin element containing the pdf viewer.
  */
 function PDFScriptingAPI(window, plugin) {
-  this.loaded_ = false;
   this.pendingScriptingMessages_ = [];
   this.setPlugin(plugin);
 
   window.addEventListener('message', function(event) {
     if (event.origin != 'chrome-extension://mhjfbmdgcfjbbpaeojofohoefgiehjai') {
       console.error('Received message that was not from the extension: ' +
                     event);
       return;
     }
     switch (event.data.type) {
       case 'viewport':
         if (this.viewportChangedCallback_)
           this.viewportChangedCallback_(event.data.pageX,
                                         event.data.pageY,
                                         event.data.pageWidth,
                                         event.data.viewportWidth,
                                         event.data.viewportHeight);
         break;
       case 'documentLoaded':
-        this.loaded_ = true;
-        if (this.loadCallback_)
+        if (this.loadCallback_) {
           this.loadCallback_();
+          this.loadCallback_ = null;
+        }
         break;
       case 'getAccessibilityJSONReply':
         if (this.accessibilityCallback_) {
           this.accessibilityCallback_(event.data.json);
           this.accessibilityCallback_ = null;
         }
         break;
       case 'getSelectedTextReply':
         if (this.selectedTextCallback_) {
           this.selectedTextCallback_(event.data.selectedText);
@@ skipping 20 matching lines @@
   },
 
  /**
   * Sets the plugin element containing the PDF viewer. The element will usually
   * be passed into the PDFScriptingAPI constructor but may also be set later.
   * @param {Object} plugin the plugin element containing the PDF viewer.
   */
   setPlugin: function(plugin) {
     this.plugin_ = plugin;
 
-    // Send an initialization message to the plugin indicating the window to
-    // respond to.
     if (this.plugin_) {
-      this.sendMessage_({
-        type: 'setParentWindow'
-      });
-
-      // Now we can flush pending messages
+      // Flush pending messages.
       while (this.pendingScriptingMessages_.length > 0)
         this.sendMessage_(this.pendingScriptingMessages_.shift());
     }
   },
 
   /**
    * Sets the callback which will be run when the PDF viewport changes.
    * @param {Function} callback the callback to be called.
    */
   setViewportChangedCallback: function(callback) {
     this.viewportChangedCallback_ = callback;
   },
 
   /**
    * 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.
+   * @return {boolean} false if there is a callback already set and true
+   *     otherwise.
    */
   setLoadCallback: function(callback) {
+    if (this.loadCallback_)
+      return false;
     this.loadCallback_ = callback;
-    if (this.loaded_ && callback)
-      callback();
+    this.sendMessage_({
+      type: 'isDocumentLoaded'
+    });
+    return true;
   },
 
   /**
    * Resets the PDF viewer into print preview mode.
    * @param {string} url the url of the PDF to load.
    * @param {boolean} grayscale whether or not to display the PDF in grayscale.
    * @param {Array.<number>} pageNumbers an array of the page numbers.
    * @param {boolean} modifiable whether or not the document is modifiable.
    */
   resetPrintPreviewMode: function(url, grayscale, pageNumbers, modifiable) {
@@ skipping 110 matching lines @@
   };
   // Add the functions to the iframe so that they can be called directly.
   iframe.setViewportChangedCallback =
       client.setViewportChangedCallback.bind(client);
   iframe.setLoadCallback = client.setLoadCallback.bind(client);
   iframe.resetPrintPreviewMode = client.resetPrintPreviewMode.bind(client);
   iframe.loadPreviewPage = client.loadPreviewPage.bind(client);
   iframe.sendKeyEvent = client.sendKeyEvent.bind(client);
   return iframe;
 }