Fix css-poll-style-updates test race condition in MSAN

Failing bot: https://ci.chromium.org/p/chromium/builders/ci/WebKit%20Linux%20MSAN

Bug: chromium:1113314
Change-Id: If00935628d5ef204be4d4ecfec58ae7991d9de61
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2339657Reviewed-by: Andrey Kosyakov <caseq@chromium.org>
Commit-Queue: Andrey Kosyakov <caseq@chromium.org>
Cr-Commit-Position: refs/heads/master@{#795221}

third_party/blink/web_tests/inspector-protocol/css/css-poll-style-updates.js

@@ -116,14 +116,16 @@
     `Updated nodes from the second session should not contain the fourth item: ${
     !secondSessionRespondedIds.includes(secondSessionNodeIds[3])}`);
 
+  const multipleRequestsPromise = Promise.all([
+    firstDP.CSS.takeComputedStyleUpdates(),
+    firstDP.CSS.takeComputedStyleUpdates(),
+  ]);
+
   firstSession.evaluate(
     () =>
       document.querySelector('.container').classList.remove('change-2'));
   // Only one request can be active at a time; other requests should fail.
-  const multipleRequestsResponse = await Promise.all([
-    firstDP.CSS.takeComputedStyleUpdates(),
-    firstDP.CSS.takeComputedStyleUpdates(),
-  ]);
+  const multipleRequestsResponse = await multipleRequestsPromise;
   let errorResponse =
     multipleRequestsResponse.find(result => Boolean(result.error));
   testRunner.log(