Extend the hang monitor timeout when an event ack is received.

content/browser/renderer_host/render_widget_host_impl.cc

Index: content/browser/renderer_host/render_widget_host_impl.cc
diff --git a/content/browser/renderer_host/render_widget_host_impl.cc b/content/browser/renderer_host/render_widget_host_impl.cc
index 0de4c1ccee5673c27c9c669932b0a384c714e02b..3d48995854539b740f4abf044e02d3c659d31ecb 100644
--- a/content/browser/renderer_host/render_widget_host_impl.cc
+++ b/content/browser/renderer_host/render_widget_host_impl.cc
@@ -1779,9 +1779,13 @@ void RenderWidgetHostImpl::IncrementInFlightEventCount() {
 
 void RenderWidgetHostImpl::DecrementInFlightEventCount() {
   DCHECK_GE(in_flight_event_count_, 0);
-  // Cancel pending hung renderer checks since the renderer is responsive.
-  if (decrement_in_flight_event_count() <= 0)
+  if (decrement_in_flight_event_count() <= 0) {
+    // Cancel pending hung renderer checks since the renderer is responsive.
     StopHangMonitorTimeout();
+  } else {
+    // The renderer is responsive, but there are in-flight events to wait for.
+    RestartHangMonitorTimeout();
+  }
 }
 
 void RenderWidgetHostImpl::OnHasTouchEventHandlers(bool has_handlers) {