Use promise in wpt pointer event tests to finish the tests

Instead of adding a variable to check if the test is finished, we can
create a promise object and finish the test at its last callback.

Bug: 606367
Change-Id: Iabf281a1fffca85630683e79436a8b442057b824
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1618002
Commit-Queue: Lan Wei <lanwei@chromium.org>
Reviewed-by: Navid Zolghadr <nzolghadr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#663936}

third_party/blink/web_tests/external/wpt/pointerevents/pointerevent_touch-action-inherit_child-auto-child-none_touch.html

@@ -92,7 +92,7 @@
             function run() {
                 var target0 = document.getElementById("target0");
                 var btnComplete = document.getElementById("btnComplete");
-                var clickIsReceived = false;
+                var actions_promise;
 
                 // Check if touch-action attribute works properly for embedded divs
                 // Scrollable-Parent, Child: `auto`, Grand-Child: `none`
@@ -103,7 +103,11 @@
                         assert_equals(target0.scrollLeft, 0, "scroll x offset should be 0 in the end of the test");
                         assert_equals(target0.scrollTop, 0, "scroll y offset should be 0 in the end of the test");
                     });
-                    clickIsReceived = true;
+
+                    // Make sure the test finishes after all the input actions are completed.
+                    actions_promise.then( () => {
+                      test_touchaction.done();
+                    });
                     updateDescriptionComplete();
                 });
 
@@ -112,15 +116,11 @@
                 });
 
                 // Inject touch inputs.
-                touchScrollInTarget(scrollTarget, 'down').then(function() {
-                    return touchScrollInTarget(scrollTarget, 'right');
-                }).then(function() {
-                    return clickInTarget("touch", btnComplete);
+                actions_promise = touchScrollInTarget(scrollTarget, 'down');
+                actions_promise.then(function() {
+                    touchScrollInTarget(scrollTarget, 'right');
                 }).then(function() {
-                    test_touchaction.step(function () {
-                        assert_true(clickIsReceived, "click should be received before the test finishes");
-                    }, "click should be received before the test finishes");
-                    test_touchaction.done();
+                    clickInTarget("touch", btnComplete);
                 });
             }
         </script>