Interactive forms: rewrite AcroForms example

This patch lets the AcroForms example make use of the built-in interactive
forms functionality in PDF.js. This makes the example:

- much easier to understand;
- more feature-complete;
- in sync with the core when new functionality is added;
- similar to the other examples in terms of structure.

examples/acroforms/acroforms.js

@@ -0,0 +1,49 @@
+/* Copyright 2017 Mozilla Foundation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+'use strict';
+
+PDFJS.workerSrc = '../../build/dist/build/pdf.worker.js';
+
+var DEFAULT_URL = '../../test/pdfs/f1040.pdf';
+var DEFAULT_SCALE = 1.0;
+
+var container = document.getElementById('pageContainer');
+
+// Fetch the PDF document from the URL using promises.
+PDFJS.getDocument(DEFAULT_URL).then(function (doc) {
+  // Use a promise to fetch and render the next page.
+  var promise = Promise.resolve();
+
+  for (var i = 1; i <= doc.numPages; i++) {
+    promise = promise.then(function (pageNum) {
+      return doc.getPage(pageNum).then(function (pdfPage) {
+        // Create the page view.
+        var pdfPageView = new PDFJS.PDFPageView({
+          container: container,
+          id: pageNum,
+          scale: DEFAULT_SCALE,
+          defaultViewport: pdfPage.getViewport(DEFAULT_SCALE),
+          annotationLayerFactory: new PDFJS.DefaultAnnotationLayerFactory(),
+          renderInteractiveForms: true,
+        });
+
+        // Associate the actual page with the view and draw it.
+        pdfPageView.setPdfPage(pdfPage);
+        return pdfPageView.draw();
+      });
+    }.bind(null, i));
+  }
+});