Fixed failing content_browsertests when async wheel events is on.

content/browser/site_per_process_browsertest.cc

Index: content/browser/site_per_process_browsertest.cc
diff --git a/content/browser/site_per_process_browsertest.cc b/content/browser/site_per_process_browsertest.cc
index ee5c40f911d8a41ffbab964a9c797b1cb69a9d76..4bc502bb0805a65a23fa7e445ae1d896c72d6b79 100644
--- a/content/browser/site_per_process_browsertest.cc
+++ b/content/browser/site_per_process_browsertest.cc
@@ -64,6 +64,7 @@
 #include "content/public/browser/notification_types.h"
 #include "content/public/browser/resource_dispatcher_host.h"
 #include "content/public/common/browser_side_navigation_policy.h"
+#include "content/public/common/content_features.h"
 #include "content/public/common/content_switches.h"
 #include "content/public/common/url_constants.h"
 #include "content/public/test/browser_test_utils.h"
@@ -5691,10 +5692,16 @@ class SitePerProcessMouseWheelBrowserTest : public SitePerProcessBrowserTest {
 
     SendMouseWheel(pos);
 
-    // This time only the wheel handler fires, since it prevent defaults on
-    // even numbered scrolls.
+    // If async_wheel_events is disabled, this time only the wheel handler
+    // fires, since even numbered scrolls are prevent-defaulted. If it is
+    // enabled, then this wheel event will be sent non-blockingly and won't be
+    // cancellable.
     EXPECT_TRUE(msg_queue.WaitForMessage(&reply));
     EXPECT_EQ("\"wheel: 2\"", reply);
+    if (base::FeatureList::IsEnabled(features::kAsyncWheelEvents)) {
+      EXPECT_TRUE(msg_queue.WaitForMessage(&reply));
+      EXPECT_EQ("\"scroll: 2\"", reply);
+    }
 
     SendMouseWheel(pos);