DNR: Speculatively fix flaky DeclarativeNetRequestBrowserTest.AllowAllRequests_SrcDoc.

Wait for the fetch to complete before checking whether xhr request was
seen by the browser. This should hopefully fix the flakiness since page
load won't necessarily wait for the fetch to complete.

BUG=1050536, 1056031

Change-Id: I9c043d69c4d619e00737303d2aaa3c15dc587ae2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2076658
Commit-Queue: Karan Bhatia <karandeepb@chromium.org>
Reviewed-by: Istiaque Ahmed <lazyboy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#744926}

chrome/browser/extensions/api/declarative_net_request/declarative_net_request_browsertest.cc

@@ -3880,9 +3880,8 @@ IN_PROC_BROWSER_TEST_P(DeclarativeNetRequestBrowserTest, AllowAllRequests) {
 
 // Ensure allowAllRequests rules work correctly for srcdoc frames. Regression
 // test for crbug.com/1050536.
-// TODO(crbug.com/1056031): Re-enabled this test.
 IN_PROC_BROWSER_TEST_P(DeclarativeNetRequestBrowserTest,
-                       DISABLED_AllowAllRequests_SrcDoc) {
+                       AllowAllRequests_SrcDoc) {
   TestRule block_rule = CreateGenericRule();
   block_rule.id = kMinValidID;
   block_rule.priority = kMinValidPriority;
@@ -3900,9 +3899,15 @@ IN_PROC_BROWSER_TEST_P(DeclarativeNetRequestBrowserTest,
   ASSERT_NO_FATAL_FAILURE(
       LoadExtensionWithRules({block_rule, allow_srcdoc_rule}));
 
+  content::DOMMessageQueue message_queue(web_contents());
   GURL page_url = embedded_test_server()->GetURL("/srcdoc.html");
   ui_test_utils::NavigateToURL(browser(), page_url);
 
+  // Wait for the fetch to complete.
+  std::string message;
+  ASSERT_TRUE(message_queue.WaitForMessage(&message));
+  EXPECT_EQ("\"failure\"", message) << message;
+
   const std::set<GURL> requests_seen = GetAndResetRequestsToServer();
   EXPECT_TRUE(base::Contains(requests_seen, page_url));
 

chrome/test/data/extensions/declarative_net_request/srcdoc.html

@@ -8,8 +8,11 @@
 
     // The fetch below will fail eventually, but the request will reach the
     // browser.
-    frame.contentWindow.fetch('subresources/xhr_target.txt')
-      .catch((error) => {});
+    frame.contentWindow.fetch('subresources/xhr_target.txt').then(() => {
+      domAutomationController.send('success');
+    }, () => {
+      domAutomationController.send('failure');
+    });
 </script>
 
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