feat(Page): teach Page.setContent to wait for resources to load

This patch adds "options" parameter to the `page.setContent` method. The
parameter is the same as a navigation parameter and allows to specify
maximum timeout to wait for resources to be loaded, as well as to
describe events that should be emitted before the setContent operation
would be considered successful.

Fixes puppeteer#728.

docs/api.md

@@ -937,9 +937,16 @@ page.select('select#colors', 'blue'); // single selection
 page.select('select#colors', 'red', 'green', 'blue'); // multiple selections
 ```
 
-#### page.setContent(html)
+#### page.setContent(html, options)
 - `html` <[string]> HTML markup to assign to the page.
-- returns: <[Promise]>
+- `options` <[Object]> Navigation parameters which might have the following properties:
+  - `timeout` <[number]> Maximum navigation time in milliseconds, defaults to 30 seconds, pass `0` to disable timeout.
+  - `waitUntil` <[string]|[Array]<[string]>> When to consider setting content complete, defaults to `load`. Given an array of event strings, setting content is considered to be successful after all events have been fired. Events Can be either:
+    - `load` - consider setting content to be finished when the `load` event is fired.
+    - `domcontentloaded` - consider setting content to be finished when the `DOMContentLoaded` event is fired.
+    - `networkidle0` - consider setting content to be finished when there are no more then 0 network connections for at least `500` ms.
+    - `networkidle2` - consider setting content to be finished when there are no more then 2 network connections for at least `500` ms.
+- returns: <[Promise]> Promise which resolves when content is set and all events are triggered.
 
 #### page.setCookie(...cookies)
 - `...cookies` <...[Object]>

lib/Page.js

@@ -437,13 +437,17 @@ class Page extends EventEmitter {
 
   /**
    * @param {string} html
+   * @param {!Object=} options
    */
-  async setContent(html) {
-    await this.evaluate(html => {
-      document.open();
-      document.write(html);
-      document.close();
-    }, html);
+  async setContent(html, options) {
+    await Promise.all([
+      this.evaluate(html => {
+        document.open();
+        document.write(html);
+        document.close();
+      }, html),
+      this.waitForNavigation(options),
+    ]);
   }
 
   /**

test/test.js

@@ -2174,6 +2174,17 @@ describe('Page', function() {
       const result = await page.content();
       expect(result).toBe(`${doctype}${expectedOutput}`);
     }));
+    it('should await resources to load', SX(async function() {
+      const imgPath = '/img.png';
+      let imgResponse = null;
+      server.setRoute(imgPath, (req, res) => imgResponse = res);
+      let loaded = false;
+      let contentPromise = page.setContent(`<img src="${PREFIX + imgPath}"></img>`).then(() => loaded = true);
+      await server.waitForRequest(imgPath);
+      expect(loaded).toBe(false);
+      imgResponse.end();
+      await contentPromise;
+    }));
   });
 
   describe('Network Events', function() {