Deflake TouchActionAckTimeout

Currently this test is flaky because we do not wait for the ack of the
touch start from the main thread.

This CL fixes this issue by using a ack waiter, to ensure that the ack
from the main thread has arrived.

TBR=alexmos@chromium.org

Bug: 871062
Change-Id: Ia883bcbb1b483d8fb481ce88dd5c947ea623d506
Reviewed-on: https://chromium-review.googlesource.com/1221476
Commit-Queue: Xida Chen <xidachen@chromium.org>
Reviewed-by: James MacLean <wjmaclean@chromium.org>
Cr-Commit-Position: refs/heads/master@{#591271}

content/browser/site_per_process_hit_test_browsertest.cc

@@ -1506,33 +1506,12 @@ IN_PROC_BROWSER_TEST_P(SitePerProcessEmulatedTouchBrowserTest,
   RunTest(TouchActionBubbling);
 }
 
-#if defined(OS_ANDROID)
-namespace {
-// This function is used in TouchActionAckTimeout and
-// SubframeGestureEventRouting, which is defined either under Android or Aura.
-void OnSyntheticGestureCompleted(scoped_refptr<MessageLoopRunner> runner,
-                                 SyntheticGesture::Result result) {
-  EXPECT_EQ(SyntheticGesture::GESTURE_FINISHED, result);
-  runner->Quit();
-}
-
-void GiveItSomeTime(int t) {
-  base::RunLoop run_loop;
-  base::ThreadTaskRunnerHandle::Get()->PostDelayedTask(
-      FROM_HERE, run_loop.QuitClosure(), base::TimeDelta::FromMilliseconds(t));
-  run_loop.Run();
-}
-
-}  // namespace
-#endif  // defined(OS_ANDROID)
-
 // Regression test for https://crbug.com/851644. The test passes as long as it
 // doesn't crash.
 // Touch action ack timeout is enabled on Android only.
-// Flaky, see https://crbug.com/871062.
 #if defined(OS_ANDROID)
 IN_PROC_BROWSER_TEST_P(SitePerProcessHitTestBrowserTest,
-                       DISABLED_TouchActionAckTimeout) {
+                       TouchActionAckTimeout) {
   GURL main_url(
       embedded_test_server()->GetURL("/frame_tree/page_with_janky_frame.html"));
   ASSERT_TRUE(NavigateToURL(shell(), main_url));
@@ -1566,41 +1545,29 @@ IN_PROC_BROWSER_TEST_P(SitePerProcessHitTestBrowserTest,
   params.gesture_source_type = SyntheticGestureParams::TOUCH_INPUT;
   params.anchor = gfx::PointF(point_in_child.x(), point_in_child.y());
   params.distances.push_back(gfx::Vector2dF(0, -10));
-  // Make this scroll slow so that the second scroll will be queued even before
-  // this one ends.
-  params.speed_in_pixels_s = 1000;
+  // The JS jank from the "page_with_touch_start_janking_main_thread.html"
+  // causes the touch ack timeout. Set the speed high so that the gesture can be
+  // completed quickly and so does this test.
+  params.speed_in_pixels_s = 100000;
   std::unique_ptr<SyntheticSmoothScrollGesture> gesture(
       new SyntheticSmoothScrollGesture(params));
 
-  scoped_refptr<MessageLoopRunner> runner = new MessageLoopRunner();
+  InputEventAckWaiter ack_observer(
+      child_frame_host->GetRenderWidgetHost(),
+      base::BindRepeating([](content::InputEventAckSource source,
+                             content::InputEventAckState state,
+                             const blink::WebInputEvent& event) {
+        return event.GetType() == blink::WebGestureEvent::kGestureScrollEnd;
+      }));
+  ack_observer.Reset();
+
   RenderWidgetHostImpl* render_widget_host =
       root->current_frame_host()->GetRenderWidgetHost();
   render_widget_host->QueueSyntheticGesture(
-      std::move(gesture), base::BindOnce(OnSyntheticGestureCompleted, runner));
-  // The first gesture takes 100ms, so wait for 120ms to ensure that it has
-  // finished.
-  runner->Run();
-  GiveItSomeTime(120);
-
-  SyntheticSmoothScrollGestureParams params2;
-  params2.gesture_source_type = SyntheticGestureParams::TOUCH_INPUT;
-  params2.anchor = gfx::PointF(point_in_child.x(), point_in_child.y());
-  params2.distances.push_back(gfx::Vector2dF(0, -10));
-  params2.speed_in_pixels_s = 100000;
-  std::unique_ptr<SyntheticSmoothScrollGesture> gesture2(
-      new SyntheticSmoothScrollGesture(params2));
-  render_widget_host->QueueSyntheticGesture(
-      std::move(gesture2), base::BindOnce(OnSyntheticGestureCompleted, runner));
-
-  runner->Run();
-  runner = nullptr;
-
-  // Give enough time to make sure all gesture are flushed and handled.
-  base::RunLoop run_loop;
-  base::ThreadTaskRunnerHandle::Get()->PostDelayedTask(
-      FROM_HERE, run_loop.QuitClosure(),
-      base::TimeDelta::FromMilliseconds(2500));
-  run_loop.Run();
+      std::move(gesture), base::BindOnce([](SyntheticGesture::Result result) {
+        EXPECT_EQ(SyntheticGesture::GESTURE_FINISHED, result);
+      }));
+  ack_observer.Wait();
 }
 #endif  // defined(OS_ANDROID)