Fix race in softnavs WPT interaction-with-paint-before-back.tentative.html. (#52259)

Same pattern as cr/6499490: We should create the promise before
the click, so that we don't miss the softnavs perf entry.

I'm thinking this means we can re-enable the test in the
expectations.

Change-Id: Ie6ffbc9eea4319ce1a6e12ef262459aab550681b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6500153
Reviewed-by: Annie Sullivan <sullivan@chromium.org>
Commit-Queue: Johannes Henkel <johannes@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1453644}

Co-authored-by: Johannes Henkel <johannes@chromium.org>

Author: chromium-wpt-export-bot

soft-navigation-heuristics/interaction-with-paint-before-back.tentative.html

@@ -47,10 +47,11 @@
         history.back();
       });
       promise_test(async t => {
+        const soft_nav_promise = waitOnSoftNav();
         if (test_driver) {
           test_driver.click(link);
         }
-        await waitOnSoftNav();
+        await soft_nav_promise;
         assert_equals(
             document.softNavigations, 1,
             'Single Soft Navigation detected');
@@ -70,7 +71,3 @@
   </script>
 </body>
 </html>
-
-
-
-