Fix flakyness in broadcastchannel/blobs.html test.

third_party/WebKit/LayoutTests/broadcastchannel/blobs.html

Index: third_party/WebKit/LayoutTests/broadcastchannel/blobs.html
diff --git a/third_party/WebKit/LayoutTests/broadcastchannel/blobs.html b/third_party/WebKit/LayoutTests/broadcastchannel/blobs.html
index a75be5e0e897501ed0ba2d62b9c54373502dab98..041d8022ac4240a78bb2242e94b1a66233702014 100644
--- a/third_party/WebKit/LayoutTests/broadcastchannel/blobs.html
+++ b/third_party/WebKit/LayoutTests/broadcastchannel/blobs.html
@@ -5,9 +5,9 @@
 <script>
 
 async_test(t => {
-    let c1 = new BroadcastChannel('blob');
-    let c2 = new BroadcastChannel('blob');
-    let c3 = new BroadcastChannel('blob');
+    const c1 = new BroadcastChannel('blob');
+    const c2 = new BroadcastChannel('blob');
+    const c3 = new BroadcastChannel('blob');
 
     let readCount = 0;
     c2.onmessage = t.step_func(e => {
@@ -15,7 +15,7 @@ async_test(t => {
         assert_true('blob' in e.data);
         assert_true(e.data.blob instanceof Blob);
         assert_equals(e.data.blob.size, 6);
-        let reader = new FileReader();
+        const reader = new FileReader();
         reader.onerror = t.unreached_func();
         reader.onload = t.step_func(() => {
             assert_equals(reader.result, 'foobar');
@@ -29,19 +29,11 @@ async_test(t => {
   }, 'Blobs work on BroadcastChannel');
 
 async_test(t => {
-    let c1 = new BroadcastChannel('blobworker');
-    let c2 = new BroadcastChannel('blobworker');
-    let events = [];
+    const c1 = new BroadcastChannel('blobworker');
+    const c2 = new BroadcastChannel('blobworker');
+    const events = [];
 
-    c1.onmessage = e => events.push(e.data);
-    c2.onmessage = e => events.push(e.data);
-    c2.addEventListener('message', e => {
-        if (e.data.blob)
-          c1.postMessage('done');
-      });
-
-    let worker = new Worker('resources/worker.js');
-    worker.onmessage = t.step_func(e => {
+    const verifyEvents = function() {
         assert_equals(events.length, 5);
         assert_equals(events[0], 'from worker');
         assert_equals(events[1], 'from worker');
@@ -50,13 +42,34 @@ async_test(t => {
         assert_true(events[3].blob instanceof Blob);
         assert_equals(events[3].blob.size, 11);
         assert_equals(events[4], 'done');
-        let reader = new FileReader();
+        const reader = new FileReader();
         reader.onerror = t.unreached_func();
         reader.onload = t.step_func(() => {
             assert_equals(reader.result, 'hello-world');
             t.done();
           });
         reader.readAsText(events[3].blob);
+    };
+
+    let receivedDone = false;
+    let receivedWorkerDone = false;
+
+    c1.onmessage = e => events.push(e.data);
+    c2.onmessage = e => events.push(e.data);
+    c2.addEventListener('message', t.step_func(e => {
+        if (e.data.blob)
+          c1.postMessage('done');
+        if (e.data === 'done')
+          receivedDone = true;
+        if (receivedDone && receivedWorkerDone)
+          verifyEvents();
+      }));
+
+    const worker = new Worker('resources/worker.js');
+    worker.onmessage = t.step_func(e => {
+        receivedWorkerDone = true;
+        if (receivedDone && receivedWorkerDone)
+          verifyEvents();
       });
     worker.postMessage({channel: 'blobworker'});
     worker.postMessage({blob: ['hello-world']});