Test only. Fix quic e2e test flakiness caused by quic_buffer_packet_till_chlo.

net/tools/quic/end_to_end_test.cc

Index: net/tools/quic/end_to_end_test.cc
diff --git a/net/tools/quic/end_to_end_test.cc b/net/tools/quic/end_to_end_test.cc
index 286bd15fd284c27c2af0c88dc75a54c148e66882..efbd78795a18addf812e61ae017c57399c3ef97e 100644
--- a/net/tools/quic/end_to_end_test.cc
+++ b/net/tools/quic/end_to_end_test.cc
@@ -102,7 +102,8 @@ struct TestParams {
              QuicTag congestion_control_tag,
              bool disable_hpack_dynamic_table,
              bool force_hol_blocking,
-             bool use_cheap_stateless_reject)
+             bool use_cheap_stateless_reject,
+             bool buffer_packet_till_chlo)
       : client_supported_versions(client_supported_versions),
         server_supported_versions(server_supported_versions),
         negotiated_version(negotiated_version),
@@ -112,7 +113,8 @@ struct TestParams {
         congestion_control_tag(congestion_control_tag),
         disable_hpack_dynamic_table(disable_hpack_dynamic_table),
         force_hol_blocking(force_hol_blocking),
-        use_cheap_stateless_reject(use_cheap_stateless_reject) {}
+        use_cheap_stateless_reject(use_cheap_stateless_reject),
+        buffer_packet_till_chlo(buffer_packet_till_chlo) {}
 
   friend ostream& operator<<(ostream& os, const TestParams& p) {
     os << "{ server_supported_versions: "
@@ -128,8 +130,8 @@ struct TestParams {
        << QuicUtils::TagToString(p.congestion_control_tag);
     os << " disable_hpack_dynamic_table: " << p.disable_hpack_dynamic_table;
     os << " force_hol_blocking: " << p.force_hol_blocking;
-    os << " use_cheap_stateless_reject: " << p.use_cheap_stateless_reject
-       << " }";
+    os << " use_cheap_stateless_reject: " << p.use_cheap_stateless_reject;
+    os << " buffer_packet_till_chlo: " << p.buffer_packet_till_chlo << " }";
     return os;
   }
 
@@ -142,6 +144,7 @@ struct TestParams {
   bool disable_hpack_dynamic_table;
   bool force_hol_blocking;
   bool use_cheap_stateless_reject;
+  bool buffer_packet_till_chlo;
 };
 
 // Constructs various test permutations.
@@ -180,7 +183,7 @@ vector<TestParams> GetTestParams() {
 
   // This must be kept in sync with the number of nested for-loops below as it
   // is used to prune the number of tests that are run.
-  const int kMaxEnabledOptions = 5;
+  const int kMaxEnabledOptions = 6;
   int max_enabled_options = 0;
   vector<TestParams> params;
   for (bool server_uses_stateless_rejects_if_peer_supported : {true, false}) {
@@ -189,75 +192,90 @@ vector<TestParams> GetTestParams() {
         for (bool disable_hpack_dynamic_table : {false}) {
           for (bool force_hol_blocking : {true, false}) {
             for (bool use_cheap_stateless_reject : {true, false}) {
-              int enabled_options = 0;
-              if (force_hol_blocking) {
-                ++enabled_options;
-              }
-              if (congestion_control_tag != kQBIC) {
-                ++enabled_options;
-              }
-              if (disable_hpack_dynamic_table) {
-                ++enabled_options;
-              }
-              if (client_supports_stateless_rejects) {
-                ++enabled_options;
-              }
-              if (server_uses_stateless_rejects_if_peer_supported) {
-                ++enabled_options;
-              }
-              if (use_cheap_stateless_reject) {
-                ++enabled_options;
-              }
-              CHECK_GE(kMaxEnabledOptions, enabled_options);
-              if (enabled_options > max_enabled_options) {
-                max_enabled_options = enabled_options;
-              }
-
-              // Run tests with no options, a single option, or all the
-              // options enabled to avoid a combinatorial explosion.
-              if (enabled_options > 1 && enabled_options < kMaxEnabledOptions) {
-                continue;
-              }
-
-              for (const QuicVersionVector& client_versions : version_buckets) {
-                CHECK(!client_versions.empty());
-                // Add an entry for server and client supporting all versions.
-                params.push_back(TestParams(
-                    client_versions, all_supported_versions,
-                    client_versions.front(), client_supports_stateless_rejects,
-                    server_uses_stateless_rejects_if_peer_supported,
-                    congestion_control_tag, disable_hpack_dynamic_table,
-                    force_hol_blocking, use_cheap_stateless_reject));
-
-                // Run version negotiation tests tests with no options, or all
-                // the options enabled to avoid a combinatorial explosion.
-                if (enabled_options > 0 &&
+              for (bool buffer_packet_till_chlo : {true, false}) {
+                if (!buffer_packet_till_chlo && use_cheap_stateless_reject) {
+                  // Doing stateless reject while not buffering packet
+                  // before CHLO is not allowed.
+                  break;
+                }
+                int enabled_options = 0;
+                if (force_hol_blocking) {
+                  ++enabled_options;
+                }
+                if (congestion_control_tag != kQBIC) {
+                  ++enabled_options;
+                }
+                if (disable_hpack_dynamic_table) {
+                  ++enabled_options;
+                }
+                if (client_supports_stateless_rejects) {
+                  ++enabled_options;
+                }
+                if (server_uses_stateless_rejects_if_peer_supported) {
+                  ++enabled_options;
+                }
+                if (buffer_packet_till_chlo) {
+                  ++enabled_options;
+                }
+                if (use_cheap_stateless_reject) {
+                  ++enabled_options;
+                }
+                CHECK_GE(kMaxEnabledOptions, enabled_options);
+                if (enabled_options > max_enabled_options) {
+                  max_enabled_options = enabled_options;
+                }
+
+                // Run tests with no options, a single option, or all the
+                // options enabled to avoid a combinatorial explosion.
+                if (enabled_options > 1 &&
                     enabled_options < kMaxEnabledOptions) {
                   continue;
                 }
 
-                // Test client supporting all versions and server supporting 1
-                // version. Simulate an old server and exercise version
-                // downgrade in the client. Protocol negotiation should occur.
-                // Skip the i = 0 case because it is essentially the same as
-                // the default case.
-                for (size_t i = 1; i < client_versions.size(); ++i) {
-                  QuicVersionVector server_supported_versions;
-                  server_supported_versions.push_back(client_versions[i]);
+                for (const QuicVersionVector& client_versions :
+                     version_buckets) {
+                  CHECK(!client_versions.empty());
+                  // Add an entry for server and client supporting all versions.
                   params.push_back(TestParams(
-                      client_versions, server_supported_versions,
-                      server_supported_versions.front(),
+                      client_versions, all_supported_versions,
+                      client_versions.front(),
                       client_supports_stateless_rejects,
                       server_uses_stateless_rejects_if_peer_supported,
                       congestion_control_tag, disable_hpack_dynamic_table,
-                      force_hol_blocking, use_cheap_stateless_reject));
-                }  // End of version for loop.
-              }    // End of 2nd version for loop.
-            }      // End of use_cheap_stateless_reject for loop.
-          }        // End of force_hol_blocking loop.
-        }          // End of disable_hpack_dynamic_table for loop.
-      }            // End of congestion_control_tag for loop.
-    }              // End of client_supports_stateless_rejects for loop.
+                      force_hol_blocking, use_cheap_stateless_reject,
+                      buffer_packet_till_chlo));
+
+                  // Run version negotiation tests tests with no options, or all
+                  // the options enabled to avoid a combinatorial explosion.
+                  if (enabled_options > 0 &&
+                      enabled_options < kMaxEnabledOptions) {
+                    continue;
+                  }
+
+                  // Test client supporting all versions and server supporting 1
+                  // version. Simulate an old server and exercise version
+                  // downgrade in the client. Protocol negotiation should occur.
+                  // Skip the i = 0 case because it is essentially the same as
+                  // the default case.
+                  for (size_t i = 1; i < client_versions.size(); ++i) {
+                    QuicVersionVector server_supported_versions;
+                    server_supported_versions.push_back(client_versions[i]);
+                    params.push_back(TestParams(
+                        client_versions, server_supported_versions,
+                        server_supported_versions.front(),
+                        client_supports_stateless_rejects,
+                        server_uses_stateless_rejects_if_peer_supported,
+                        congestion_control_tag, disable_hpack_dynamic_table,
+                        force_hol_blocking, use_cheap_stateless_reject,
+                        buffer_packet_till_chlo));
+                  }  // End of version for loop.
+                }    // End of 2nd version for loop.
+              }      // End of buffer_packet_till_chlo loop.
+            }        // End of use_cheap_stateless_reject for loop.
+          }          // End of force_hol_blocking loop.
+        }            // End of disable_hpack_dynamic_table for loop.
+      }              // End of congestion_control_tag for loop.
+    }                // End of client_supports_stateless_rejects for loop.
     CHECK_EQ(kMaxEnabledOptions, max_enabled_options);
   }  // End of server_uses_stateless_rejects_if_peer_supported for loop.
   return params;
@@ -448,6 +466,7 @@ class EndToEndTest : public ::testing::TestWithParam<TestParams> {
   }
 
   void StartServer() {
+    FLAGS_quic_buffer_packet_till_chlo = GetParam().buffer_packet_till_chlo;
     FLAGS_quic_use_cheap_stateless_rejects =
         GetParam().use_cheap_stateless_reject;
     server_thread_.reset(new ServerThread(