Fix two memory leaks.

test/driver.js

@@ -56,23 +56,31 @@ function load() {
 }
 
 function cleanup() {
+  // Clear out all the stylesheets since a new one is created for each font.
+  while (document.styleSheets.length > 0) {
     var styleSheet = document.styleSheets[0];
     if (styleSheet) {
       while (styleSheet.cssRules.length > 0)
         styleSheet.deleteRule(0);
     }
+    var parent = styleSheet.ownerNode.parentNode;
+    parent.removeChild(styleSheet.ownerNode);
+  }
   var guard = document.getElementById('content-end');
   var body = document.body;
   while (body.lastChild !== guard)
     body.removeChild(body.lastChild);
+
+  // Wipe out the link to the pdfdoc so it can be GC'ed.
+  for (var i = 0; i < manifest.length; i++) {
+    if (manifest[i].pdfDoc) {
+      manifest[i].pdfDoc.destroy();
+      delete manifest[i].pdfDoc
+    }
+  }
 }
 
 function nextTask() {
-  // If there is a pdfDoc on the last task executed, destroy it to free memory.
-  if (task && task.pdfDoc) {
-    task.pdfDoc.destroy();
-    delete task.pdfDoc;
-  }
   cleanup();
 
   if (currentTaskIdx == manifest.length) {