function createPluginPage(pluginDir, isLocal) {
  const packageJson = require(resolveApp(`plugins/${pluginDir}/package.json`));
  const initialPath = path.join('plugins', pluginDir, 'test', 'index.html');
  const initialContents = fs.readFileSync(initialPath).toString();

  let contents = injectHeader(
    initialContents,
    `${packageJson.name} Demo`,
    isLocal,
  );
  contents = injectPluginNavBar(contents, packageJson, pluginDir, isLocal);
  contents = injectFooter(contents);

  const dirPath = path.join('gh-pages', 'plugins', pluginDir, 'test');
  fs.mkdirSync(dirPath, {recursive: true});
  fs.writeFileSync(path.join(dirPath, 'index.html'), contents, 'utf-8');
}
Create the index.html page for the plugin's page on github pages.
This page has the plugin's test playground, but wraps it in a
devsite-style header and footer, and includes the plugin's readme and
links to the plugin source files on GitHub and published package on npm.
@param {string} pluginDir The directory of the plugin that is currently
    being prepared.
@param {boolean} isLocal True if building for a local test. False if
    building for gh-pages.