Add touchTapInTarget function for wpt touch event tests

This function is reverted from pointerevent_support.js file, but the
tests that use it are still in the wpt repository.

Bug: 606367

TBR=nzolghadr@chromium.org

Change-Id: Ifd97bab0bf411b000573056152a563f4385f2500
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1594735Reviewed-by: Lan Wei <lanwei@chromium.org>
Commit-Queue: Lan Wei <lanwei@chromium.org>
Cr-Commit-Position: refs/heads/master@{#656405}

third_party/blink/web_tests/external/wpt/pointerevents/pointerevent_support.js

@@ -285,3 +285,12 @@ function touchScrollInTarget(target, direction) {
                    .pointerUp()
                    .send();
 }
+
+function touchTapInTarget(target) {
+    return new test_driver.Actions()
+                   .addPointer("pointer1", "touch")
+                   .pointerMove(0, 0, {origin: target})
+                   .pointerDown()
+                   .pointerUp()
+                   .send();
+}