Handle test output messages that arrive before the waiter is ready.

The waitForTestResultsAsMessage function now buffers test output messages received via top.postMessage in earlyTestResults if the waiter is not yet active. This prevents missing test results that are posted very quickly after the test starts. When waitForTestResultsAsMessage is called, it first checks the buffer before setting up a waiter.

Bug: 491766258
Change-Id: Ib34bb6e87ab1036e1c52ecbcd057050dc490fe7b
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/7704616
Reviewed-by: Andrey Kosyakov <caseq@chromium.org>
Commit-Queue: Danil Somsikov <dsv@chromium.org>
Auto-Submit: Danil Somsikov <dsv@chromium.org>
Commit-Queue: Andrey Kosyakov <caseq@chromium.org>

Author: danilsomsikov

front_end/Tests.js

@@ -1086,20 +1086,36 @@
     this.takeControl({slownessFactor: 10});
   };
 
-  TestSuite.prototype.waitForTestResultsAsMessage = function() {
-    const onMessage = event => {
-      if (!event.data.testOutput) {
-        return;
-      }
-      top.removeEventListener('message', onMessage);
+  const earlyTestResults = [];
+  let testResultsWaiter = null;
+
+  top.addEventListener('message', event => {
+    if (event.data && event.data.testOutput) {
       const text = event.data.testOutput;
+      if (testResultsWaiter) {
+        testResultsWaiter(text);
+      } else {
+        earlyTestResults.push(text);
+      }
+    }
+  });
+
+  TestSuite.prototype.waitForTestResultsAsMessage = function() {
+    const handleMessage = text => {
+      testResultsWaiter = null;
       if (text === 'PASS') {
         this.releaseControl();
       } else {
         this.fail(text);
       }
     };
-    top.addEventListener('message', onMessage);
+
+    if (earlyTestResults.length) {
+      handleMessage(earlyTestResults.shift());
+      return;
+    }
+
+    testResultsWaiter = handleMessage;
     this.takeControl();
   };