Revert "Enable ServiceWorkerNavigationPreloadTest.NetworkFallback."

This reverts commit 883e2427.

Reason for revert: Still failing:
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Linux%20Tests%20%28dbg%29%281%29%2832%29/53613
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Linux%20Tests%20%28dbg%29%281%29%2832%29/53612

Original change's description:
> Enable ServiceWorkerNavigationPreloadTest.NetworkFallback.
> 
> I suspect the errors were that we were getting no preload request and
> two fallback requests, which seems plausible based on the existing
> comment. Loosen the test expectations accordingly.
> 
> Bug: 896230
> Change-Id: I539b56343d5057975352f74b482b61583174fb13
> Reviewed-on: https://chromium-review.googlesource.com/c/1288330
> Commit-Queue: Matt Falkenhagen <falken@chromium.org>
> Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#600688}

TBR=falken@chromium.org,kinuko@chromium.org

Change-Id: I7f2ac588a506f1c346db8925b4657b67b5c8b654
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 896230
Reviewed-on: https://chromium-review.googlesource.com/c/1288593Reviewed-by: Christian Dullweber <dullweber@chromium.org>
Commit-Queue: Christian Dullweber <dullweber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#600730}

content/browser/service_worker/service_worker_browsertest.cc

@@ -2071,7 +2071,9 @@ const std::string
         "            result => event.source.postMessage(result)));\n"
         "  });";
 
-IN_PROC_BROWSER_TEST_F(ServiceWorkerNavigationPreloadTest, NetworkFallback) {
+// Flaky on various bots. https://crbug.com/896230
+IN_PROC_BROWSER_TEST_F(ServiceWorkerNavigationPreloadTest,
+                       DISABLED_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.";
@@ -2099,28 +2101,21 @@ IN_PROC_BROWSER_TEST_F(ServiceWorkerNavigationPreloadTest, NetworkFallback) {
   const int request_count = GetRequestCount(kPageUrl);
   ASSERT_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]));
 
-  // So we have the following constraints:
-  // [A] At most one navigation preload request.
-  // [B] At least one and at most two fallback requests.
-  // [C] Fallback requests must occur after the navigation preload request.
-  int preload_count = 0;
-  int fallback_count = 0;
-  const auto& requests = request_log_[kPageUrl];
-  for (int i = 0; i < request_count; i++) {
-    if (HasNavigationPreloadHeader(requests[i])) {
-      // [C]
-      EXPECT_EQ(0, fallback_count);
-      EXPECT_EQ("true", GetNavigationPreloadHeader(requests[i]));
-      preload_count++;
-    } else {
-      fallback_count++;
-    }
+    // Additional fallback request when the HttpCache reissues a network
+    // request.
+    if (request_count == 3)
+      EXPECT_FALSE(HasNavigationPreloadHeader(request_log_[kPageUrl][2]));
   }
-  // [A]
-  EXPECT_TRUE(preload_count == 0 || preload_count == 1) << preload_count;
-  // [B]
-  EXPECT_TRUE(fallback_count == 1 || fallback_count == 2) << fallback_count;
 }
 
 IN_PROC_BROWSER_TEST_F(ServiceWorkerNavigationPreloadTest, SetHeaderValue) {