Revert of Remove support for Alt-Svc/Alternate Protocol Probability

net/http/http_network_session.h

Index: net/http/http_network_session.h
diff --git a/net/http/http_network_session.h b/net/http/http_network_session.h
index 3648a7a0db58da84d9d384ec61236c01582c1450..30cec77f04d48d0ec4aad019a6abd4dece195f9b 100644
--- a/net/http/http_network_session.h
+++ b/net/http/http_network_session.h
@@ -101,6 +101,9 @@
     // Whether to enable Alt-Svc entries with hostname different than that of
     // the origin.
     bool enable_alternative_service_with_different_host;
+    // Only honor alternative service entries which have a higher probability
+    // than this value.
+    double alternative_service_probability_threshold;
 
     // Enables NPN support.  Note that ALPN is always enabled.
     bool enable_npn;