Fix the testharness async test API usage

third_party/WebKit/LayoutTests/shadow-dom/v0/pointer-lock-in-shadow.html

Index: third_party/WebKit/LayoutTests/shadow-dom/v0/pointer-lock-in-shadow.html
diff --git a/third_party/WebKit/LayoutTests/shadow-dom/v0/pointer-lock-in-shadow.html b/third_party/WebKit/LayoutTests/shadow-dom/v0/pointer-lock-in-shadow.html
index 4e5ce83c4f9c8f26b5fe8b424b3ebbe75c039362..7537f01f06191d997d962986e278b71898199f1b 100644
--- a/third_party/WebKit/LayoutTests/shadow-dom/v0/pointer-lock-in-shadow.html
+++ b/third_party/WebKit/LayoutTests/shadow-dom/v0/pointer-lock-in-shadow.html
@@ -16,12 +16,9 @@
 
 <script>
 async_test((test) => {
-    document.onpointerlockerror = () => {
-        assert_true(false, 'onpointerlockerror is not expected.');
-        test.done();
-    };
+    document.onpointerlockerror = test.unreached_func('onpointerlockerror is not expected.');
 
-    document.onpointerlockchange = () => {
+    document.onpointerlockchange = test.step_func(() => {
         // Not interested in handling before or after exitPointerLock.
         if (document.pointerLockElement === null)
             return;
@@ -32,13 +29,15 @@ async_test((test) => {
 
         document.exitPointerLock();
         test.done();
-    };
+    });
 
     convertTemplatesToShadowRootsWithin(host);
 
-    assert_equals(document.pointerLockElement, null);
-    assert_equals(host.shadowRoot.pointerLockElement, null);
-    assert_equals(hostV0.shadowRoot.pointerLockElement, null);
+    test.step(() => {
+        assert_equals(document.pointerLockElement, null);
+        assert_equals(host.shadowRoot.pointerLockElement, null);
+        assert_equals(hostV0.shadowRoot.pointerLockElement, null);
+    });
 
     var canvas = hostV0.shadowRoot.querySelector('canvas');
     canvas.requestPointerLock();