Adds plumbing for always requiring handshake confirmation in 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 8559217696215011d52c245d80441f8a38d241d3..a989118415d9e012be53f51dbe447e739365f57c 100644
--- a/chrome/browser/io_thread.h
+++ b/chrome/browser/io_thread.h
@@ -187,6 +187,7 @@ class IOThread : public content::BrowserThreadDelegate {
     Optional<bool> enable_quic;
     Optional<bool> enable_quic_time_based_loss_detection;
     Optional<bool> enable_quic_port_selection;
+    Optional<bool> quic_always_require_handshake_confirmation;
     Optional<size_t> quic_max_packet_length;
     net::QuicTagVector quic_connection_options;
     Optional<std::string> quic_user_agent_id;
@@ -352,6 +353,11 @@ class IOThread : public content::BrowserThreadDelegate {
       base::StringPiece quic_trial_group,
       const VariationParameters& quic_trial_params);
 
+  // Returns true if QUIC should always require handshake confirmation during
+  // the QUIC handshake.
+  static bool ShouldQuicAlwaysRequireHandshakeConfirmation(
+      const VariationParameters& quic_trial_params);
+
   // Returns the maximum length for QUIC packets, based on any flags in
   // |command_line| or the field trial.  Returns 0 if there is an error
   // parsing any of the options, or if the default value should be used.