chrome-extensions-samples/samples/webview-samples/webview/main.js

/**
 * Listens for the app launching then creates the window
 *
 * @see http://developer.chrome.com/apps/app.window.html
 */
chrome.app.runtime.onLaunched.addListener(function() {
  chrome.app.window.create('index.html', {
    id: 'embedder',
    innerBounds: {
      width: 1430,
      height: 870
    }
  });
});