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

chrome/browser/resources/pdf/pdf_scripting_api.js

Index: chrome/browser/resources/pdf/pdf_scripting_api.js
diff --git a/chrome/browser/resources/pdf/pdf_scripting_api.js b/chrome/browser/resources/pdf/pdf_scripting_api.js
index e8dd4bca03a412020645901432979cf911758427..26d6b01f6fc0d7a19a61c5d1c8f464a579758611 100644
--- a/chrome/browser/resources/pdf/pdf_scripting_api.js
+++ b/chrome/browser/resources/pdf/pdf_scripting_api.js
@@ -9,7 +9,6 @@
  * @param {Object} plugin the plugin element containing the pdf viewer.
  */
 function PDFScriptingAPI(window, plugin) {
-  this.loaded_ = false;
   this.pendingScriptingMessages_ = [];
   this.setPlugin(plugin);
 
@@ -29,9 +28,10 @@ function PDFScriptingAPI(window, plugin) {
                                         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_) {
@@ -72,14 +72,8 @@ PDFScriptingAPI.prototype = {
   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());
     }
@@ -97,11 +91,17 @@ PDFScriptingAPI.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.
+   * @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;
   },
 
   /**