build(aio): add new post-process dgeni package

This package will allow us to do complex post-processing
on the HTML that is rendered by Nunjucks.

aio/tools/transforms/post-process-package/processors/post-process-html.spec.js

@@ -0,0 +1,62 @@
+const testPackage = require('../../helpers/test-package');
+const Dgeni = require('dgeni');
+
+describe('postProcessHtml', function() {
+  let dgeni, injector, processor;
+
+  beforeEach(function() {
+    dgeni = new Dgeni([testPackage('post-process-package', true)]);
+    injector = dgeni.configureInjector();
+    processor = injector.get('postProcessHtml');
+    processor.docTypes = ['a', 'b'];
+  });
+
+  it('should be available from the injector', () => {
+    expect(processor).toBeDefined();
+  });
+
+  it('should only process docs that match the specified docTypes', () => {
+    const elements = [];
+    const captureFirstElement = ast => {
+      elements.push(ast.children[0].tagName);
+    };
+    processor.plugins = [() => captureFirstElement];
+
+    const docs = [
+      { docType: 'a', renderedContent: '<a></a>' },
+      { docType: 'b', renderedContent: '<b></b>' },
+      { docType: 'c', renderedContent: '<c></c>' },
+      { docType: 'd', renderedContent: '<d></d>' },
+    ];
+    processor.$process(docs);
+    expect(elements).toEqual(['a', 'b']);
+  });
+
+  it('should run all the plugins on each doc', () => {
+    const capitalizeFirstElement = ast => {
+      ast.children[0].tagName = ast.children[0].tagName.toUpperCase();
+    };
+    const addOneToFirstElement = ast => {
+      ast.children[0].tagName = ast.children[0].tagName + '1';
+    };
+    const elements = [];
+    const captureFirstElement = ast => {
+      elements.push(ast.children[0].tagName);
+    };
+
+    const docs = [
+      { docType: 'a', renderedContent: '<a></a>' },
+      { docType: 'b', renderedContent: '<b></b>' },
+      { docType: 'c', renderedContent: '<c></c>' },
+      { docType: 'd', renderedContent: '<d></d>' },
+    ];
+
+    processor.plugins = [
+      () => capitalizeFirstElement,
+      () => addOneToFirstElement,
+      () => captureFirstElement
+    ];
+    processor.$process(docs);
+    expect(elements).toEqual(['A1', 'B1']);
+  });
+});