QUIC - added force_hol_blocking field trial param to enable forced HOL blocking.

net/http/http_network_session.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef NET_HTTP_HTTP_NETWORK_SESSION_H_
 #define NET_HTTP_HTTP_NETWORK_SESSION_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 160 matching lines @@
     // List of hosts for which QUIC is explicitly whitelisted.
     std::unordered_set<std::string> quic_host_whitelist;
     // If true, active QUIC sessions may be migrated onto a new network when
     // the platform indicates that the default network is changing.
     bool quic_migrate_sessions_on_network_change;
     // If true, active QUIC sessions experiencing poor connectivity may be
     // migrated onto a new network.
     bool quic_migrate_sessions_early;
     // If true, bidirectional streams over QUIC will be disabled.
     bool quic_disable_bidirectional_streams;
+    // If true, enable force HOL blocking.  For measurement purposes.
+    bool quic_force_hol_blocking;
 
     ProxyDelegate* proxy_delegate;
     // Enable support for Token Binding.
     bool enable_token_binding;
   };
 
   enum SocketPoolType {
     NORMAL_SOCKET_POOL,
     WEBSOCKET_SOCKET_POOL,
     NUM_SOCKET_POOL_TYPES
@@ skipping 100 matching lines @@
 
   NextProtoVector next_protos_;
   bool enabled_protocols_[NUM_VALID_ALTERNATE_PROTOCOLS];
 
   Params params_;
 };
 
 }  // namespace net
 
 #endif  // NET_HTTP_HTTP_NETWORK_SESSION_H_