WebTestProxy should animate the page popup

We need to begin animation frames in the WebPagePopup to trigger resize events so we let WebTestProxy call animation on the page popup as well.

BUG=409503

Review URL: https://codereview.chromium.org/603873002

Cr-Commit-Position: refs/heads/master@{#297369}

content/shell/renderer/test_runner/web_test_proxy.cc

@@ -689,6 +689,10 @@ void WebTestProxyBase::AnimateNow() {
     animate_scheduled_ = false;
     web_widget_->animate(0.0);
     web_widget_->layout();
+    if (blink::WebPagePopup* popup = web_widget_->pagePopup()) {
+      popup->animate(0.0);
+      popup->layout();
+    }
   }
 }