Enable ServiceWorkerNavigationPreloadTest.NetworkFallback.

Re-enabling with looser expectations so there is still test coverage of
this case. The failure was that the preload request came after the
fallback request. The order actually might not be guaranteed if they
are on different loading pipelines/http connections? Anyway, the
important thing is that the page loads and it's not worth investigating
more as network fallback from navigation preload is an anti-pattern.

Bug: 896230
Change-Id: Idadfc573fbbeb2c0703c3a3ffa1efef14b991614
Reviewed-on: https://chromium-review.googlesource.com/c/1290573Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Commit-Queue: Matt Falkenhagen <falken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#601581}

content/browser/service_worker/service_worker_browsertest.cc

@@ -2111,9 +2111,7 @@ const std::string
         "            result => event.source.postMessage(result)));\n"
         "  });";
 
-// Flaky on various bots. https://crbug.com/896230
-IN_PROC_BROWSER_TEST_F(ServiceWorkerNavigationPreloadTest,
-                       DISABLED_NetworkFallback) {
+IN_PROC_BROWSER_TEST_F(ServiceWorkerNavigationPreloadTest, NetworkFallback) {
   const char kPageUrl[] = "/service_worker/navigation_preload.html";
   const char kWorkerUrl[] = "/service_worker/navigation_preload.js";
   const char kPage[] = "<title>PASS</title>Hello world.";
@@ -2139,23 +2137,17 @@ IN_PROC_BROWSER_TEST_F(ServiceWorkerNavigationPreloadTest,
   //   the ongoing request, possibly triggering another network request (see
   //   https://crbug.com/876911).
   const int request_count = GetRequestCount(kPageUrl);
-  ASSERT_TRUE(request_count == 1 || request_count == 2 || request_count == 3)
+  EXPECT_TRUE(request_count == 1 || request_count == 2 || request_count == 3)
       << request_count;
-  if (request_count == 1) {
-    // Fallback request.
-    EXPECT_FALSE(HasNavigationPreloadHeader(request_log_[kPageUrl][0]));
-  } else {
-    // Navigation preload request.
-    ASSERT_TRUE(HasNavigationPreloadHeader(request_log_[kPageUrl][0]));
-    EXPECT_EQ("true", GetNavigationPreloadHeader(request_log_[kPageUrl][0]));
-    // Fallback request.
-    EXPECT_FALSE(HasNavigationPreloadHeader(request_log_[kPageUrl][1]));
 
-    // Additional fallback request when the HttpCache reissues a network
-    // request.
-    if (request_count == 3)
-      EXPECT_FALSE(HasNavigationPreloadHeader(request_log_[kPageUrl][2]));
+  // There should be at least one fallback request.
+  int fallback_count = 0;
+  const auto& requests = request_log_[kPageUrl];
+  for (int i = 0; i < request_count; i++) {
+    if (!HasNavigationPreloadHeader(requests[i]))
+      fallback_count++;
   }
+  EXPECT_GT(fallback_count, 0);
 }
 
 IN_PROC_BROWSER_TEST_F(ServiceWorkerNavigationPreloadTest, SetHeaderValue) {