Deflake content_browsertest: DoNotTrackTest using workers

Previously these tests finish before the worker is started, and
TearDownOnMainThread could be called during loading the script. After this CL,
each tests waits until the worker is ready to ensure that no task is running on
TearDownOnMainThread.

Bug: 872742
Change-Id: I5fc33048f852f6c7088f5a971a4a7d4a4ffa410b
Reviewed-on: https://chromium-review.googlesource.com/c/1337146Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Commit-Queue: Makoto Shimazu <shimazu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#608677}

content/browser/do_not_track_browsertest.cc

@@ -88,9 +88,11 @@ class DoNotTrackTest : public ContentBrowserTest {
   MockContentBrowserClient client_;
 };
 
-std::unique_ptr<net::test_server::HttpResponse> CaptureHeaderHandler(
+std::unique_ptr<net::test_server::HttpResponse>
+CaptureHeaderHandlerAndReturnScript(
     const std::string& path,
     net::test_server::HttpRequest::HeaderMap* header_map,
+    const std::string& script,
     base::OnceClosure done_callback,
     const net::test_server::HttpRequest& request) {
   GURL request_url = request.GetURL();
@@ -99,7 +101,10 @@ std::unique_ptr<net::test_server::HttpResponse> CaptureHeaderHandler(
 
   *header_map = request.headers;
   std::move(done_callback).Run();
-  return std::make_unique<net::test_server::BasicHttpResponse>();
+  auto response = std::make_unique<net::test_server::BasicHttpResponse>();
+  response->set_content_type("text/javascript");
+  response->set_content(script);
+  return response;
 }
 
 // Checks that the DNT header is not sent by default.
@@ -145,10 +150,12 @@ IN_PROC_BROWSER_TEST_F(DoNotTrackTest, DOMProperty) {
 // Checks that the DNT header is sent in a request for a dedicated worker
 // script.
 IN_PROC_BROWSER_TEST_F(DoNotTrackTest, Worker) {
+  const std::string kWorkerScript = R"(postMessage('DONE');)";
   net::test_server::HttpRequest::HeaderMap header_map;
   base::RunLoop loop;
-  embedded_test_server()->RegisterRequestHandler(base::BindRepeating(
-      &CaptureHeaderHandler, "/capture", &header_map, loop.QuitClosure()));
+  embedded_test_server()->RegisterRequestHandler(
+      base::BindRepeating(&CaptureHeaderHandlerAndReturnScript, "/capture",
+                          &header_map, kWorkerScript, loop.QuitClosure()));
   ASSERT_TRUE(embedded_test_server()->Start());
   if (!EnableDoNotTrack())
     return;
@@ -158,6 +165,9 @@ IN_PROC_BROWSER_TEST_F(DoNotTrackTest, Worker) {
 
   EXPECT_TRUE(header_map.find("DNT") != header_map.end());
   EXPECT_EQ("1", header_map["DNT"]);
+
+  // Wait until the worker script is loaded.
+  EXPECT_EQ("DONE", EvalJs(shell(), "waitForMessage();"));
 }
 
 // Checks that the DNT header is sent in a request for shared worker script.
@@ -169,10 +179,13 @@ IN_PROC_BROWSER_TEST_F(DoNotTrackTest, Worker) {
 #define MAYBE_SharedWorker SharedWorker
 #endif
 IN_PROC_BROWSER_TEST_F(DoNotTrackTest, MAYBE_SharedWorker) {
+  const std::string kWorkerScript =
+      R"(self.onconnect = e => { e.ports[0].postMessage('DONE'); };)";
   net::test_server::HttpRequest::HeaderMap header_map;
   base::RunLoop loop;
-  embedded_test_server()->RegisterRequestHandler(base::BindRepeating(
-      &CaptureHeaderHandler, "/capture", &header_map, loop.QuitClosure()));
+  embedded_test_server()->RegisterRequestHandler(
+      base::BindRepeating(&CaptureHeaderHandlerAndReturnScript, "/capture",
+                          &header_map, kWorkerScript, loop.QuitClosure()));
   ASSERT_TRUE(embedded_test_server()->Start());
   if (!EnableDoNotTrack())
     return;
@@ -183,26 +196,34 @@ IN_PROC_BROWSER_TEST_F(DoNotTrackTest, MAYBE_SharedWorker) {
 
   EXPECT_TRUE(header_map.find("DNT") != header_map.end());
   EXPECT_EQ("1", header_map["DNT"]);
+
+  // Wait until the worker script is loaded.
+  EXPECT_EQ("DONE", EvalJs(shell(), "waitForMessage();"));
 }
 
 // Checks that the DNT header is sent in a request for a service worker
 // script.
 IN_PROC_BROWSER_TEST_F(DoNotTrackTest, ServiceWorker) {
+  const std::string kWorkerScript = "// empty";
   net::test_server::HttpRequest::HeaderMap header_map;
   base::RunLoop loop;
-  embedded_test_server()->RegisterRequestHandler(base::BindRepeating(
-      &CaptureHeaderHandler, "/capture", &header_map, loop.QuitClosure()));
+  embedded_test_server()->RegisterRequestHandler(
+      base::BindRepeating(&CaptureHeaderHandlerAndReturnScript, "/capture",
+                          &header_map, kWorkerScript, loop.QuitClosure()));
   ASSERT_TRUE(embedded_test_server()->Start());
   if (!EnableDoNotTrack())
     return;
   NavigateToURL(shell(), GetURL("/service_worker/create_service_worker.html"));
-  // We only verify the request for the worker script so we don't check the
-  // result of register().
-  EXPECT_TRUE(ExecJs(shell(), "register('/capture');"));
+
+  EXPECT_EQ("DONE", EvalJs(shell(), "register('/capture');"));
   loop.Run();
 
   EXPECT_TRUE(header_map.find("DNT") != header_map.end());
   EXPECT_EQ("1", header_map["DNT"]);
+
+  // Service worker doesn't have to wait for onmessage event because
+  // navigator.serviceWorker.ready can ensure that the script load has
+  // been completed.
 }
 
 // Checks that the DNT header is preserved when fetching from a dedicated

content/test/data/workers/create_shared_worker.html

 <script>
 const params = new URLSearchParams(location.search);
 const worker = new SharedWorker(params.get('worker_url'));
+const onmessage_promise = new Promise(r => worker.port.onmessage = r);
+worker.port.start();
+async function waitForMessage() {
+  const message = await onmessage_promise;
+  return message.data;
+}
 </script>

content/test/data/workers/create_worker.html

 <script>
 const params = new URLSearchParams(location.search);
 const worker = new Worker(params.get('worker_url'));
+const onmessage_promise = new Promise(r => worker.onmessage = r);
+async function waitForMessage() {
+  const message = await onmessage_promise;
+  return message.data;
+}
 </script>