Add workaround to NetworkContextConfigurationBrowserTest.DiskCache.

When the network service is restarted, the disk cache entry may be
not be recovered, for reasons that aren't completely clear (corruption?
disk contention?), which causes the test to flake.  This CL modifies
the test to not fail in that case.

Bug: 836073
Change-Id: I3eedeceae6145b1d386749125c8232d552be8308
Reviewed-on: https://chromium-review.googlesource.com/1025646
Commit-Queue: Matt Menke <mmenke@chromium.org>
Reviewed-by: Maks Orlovich <morlovich@chromium.org>
Cr-Commit-Position: refs/heads/master@{#553177}

chrome/browser/net/network_context_configuration_browsertest.cc

@@ -38,6 +38,7 @@
 #include "mojo/public/cpp/system/data_pipe_utils.h"
 #include "net/base/filename_util.h"
 #include "net/base/host_port_pair.h"
+#include "net/base/load_flags.h"
 #include "net/base/net_errors.h"
 #include "net/http/http_response_headers.h"
 #include "net/test/embedded_test_server/controllable_http_response.h"
@@ -555,6 +556,7 @@ IN_PROC_BROWSER_TEST_P(NetworkContextConfigurationBrowserTest, DiskCache) {
       std::make_unique<network::ResourceRequest>();
   request->url = test_url;
   content::SimpleURLLoaderTestHelper simple_loader_helper;
+  request->load_flags = net::LOAD_ONLY_FROM_CACHE;
   std::unique_ptr<network::SimpleURLLoader> simple_loader =
       network::SimpleURLLoader::Create(std::move(request),
                                        TRAFFIC_ANNOTATION_FOR_TESTS);
@@ -562,16 +564,21 @@ IN_PROC_BROWSER_TEST_P(NetworkContextConfigurationBrowserTest, DiskCache) {
       loader_factory(), simple_loader_helper.GetCallback());
   simple_loader_helper.WaitForCallback();
 
-  std::string response_body = simple_loader_helper.response_body()
-                                  ? *simple_loader_helper.response_body()
-                                  : "";
-
-  // The response body from the above test should only appear in the response
-  // if there is an on-disk cache.
+  // The request should only succeed if there is an on-disk cache.
   if (GetHttpCacheType() != StorageType::kDisk) {
-    EXPECT_NE(original_response, response_body);
+    EXPECT_FALSE(simple_loader_helper.response_body());
+  } else if (GetParam().network_service_state !=
+             NetworkServiceState::kRestarted) {
+    ASSERT_TRUE(simple_loader_helper.response_body());
+    EXPECT_EQ(original_response, *simple_loader_helper.response_body());
   } else {
-    EXPECT_EQ(original_response, response_body);
+    // The network service restarted, and may or may not have recovered the
+    // cache entry. If the request succeded, though, it must return the correct
+    // result.
+    // TODO(mmenke): Is there any way to ensure the item in the cache can be
+    // recovered / the cache can be loaded in this test?
+    if (simple_loader_helper.response_body())
+      EXPECT_EQ(original_response, *simple_loader_helper.response_body());
   }
 }