Revert of Revert of Add a new enable_nonblocking_io field trial param for QUIC

chrome/browser/io_thread.h

Index: chrome/browser/io_thread.h
diff --git a/chrome/browser/io_thread.h b/chrome/browser/io_thread.h
index 9d0824546495739417940e0bfddb1dd9f686e959..c081e64df5eacfaaacb7cfc5059f4b314a9da5f8 100644
--- a/chrome/browser/io_thread.h
+++ b/chrome/browser/io_thread.h
@@ -190,6 +190,7 @@
     Optional<float> quic_load_server_info_timeout_srtt_multiplier;
     Optional<bool> quic_enable_truncated_connection_ids;
     Optional<bool> quic_enable_connection_racing;
+    Optional<bool> quic_enable_non_blocking_io;
     Optional<bool> quic_disable_disk_cache;
     Optional<int> quic_socket_receive_buffer_size;
     Optional<size_t> quic_max_packet_length;
@@ -385,6 +386,10 @@
   static bool ShouldQuicEnableConnectionRacing(
       const VariationParameters& quic_trial_params);
 
+  // Returns true if QUIC's should use non-blocking IO.
+  static bool ShouldQuicEnableNonBlockingIO(
+      const VariationParameters& quic_trial_params);
+
   // Returns true if QUIC shouldn't load QUIC server information from the disk
   // cache.
   static bool ShouldQuicDisableDiskCache(