Fix NestedPopupMenuTest for scheduler policy change

In the renderer we'd like to prioritize loading and compositing tasks
until first contentful paint.  That makes the already flaky
NestedPopupMenuTest worse.  With the new policy we sometimes get a
different pop up rect size (80x53 instead of 110x110). This seems
to be because there isn't always a layout before the mouse clicks
are sent.  Adding a call to WaitForHitTestData fixes this.


Bug: 971191
Change-Id: I70e89c74ee79cb36854e63e5f2e2c5b7e5fdff58
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1823865
Auto-Submit: Alex Clarke <alexclarke@chromium.org>
Commit-Queue: Ken Buchanan <kenrb@chromium.org>
Reviewed-by: Ken Buchanan <kenrb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#701112}

content/browser/site_per_process_hit_test_browsertest.cc

@@ -5682,6 +5682,8 @@ IN_PROC_BROWSER_TEST_P(SitePerProcessHitTestBrowserTest,
   scoped_refptr<ShowWidgetMessageFilter> filter = new ShowWidgetMessageFilter();
   c_node->current_frame_host()->GetProcess()->AddFilter(filter.get());
 
+  WaitForHitTestData(c_node->current_frame_host());
+
   // Target left-click event to child frame.
   blink::WebMouseEvent click_event(
       blink::WebInputEvent::kMouseDown, blink::WebInputEvent::kNoModifiers,