Add a probability to Alternate-Protocol support. Can be enabled either via a field trial or a command line flag.

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=281777

Review URL: https://codereview.chromium.org/339663010

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@281861 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/net/http/http_network_session.h b/net/http/http_network_session.h
index 272f96e7..e265a914 100644
--- a/net/http/http_network_session.h
+++ b/net/http/http_network_session.h
@@ -104,6 +104,7 @@
     // Noe: Using this in the case of NPN for HTTP only results in the browser
     // trying SSL and then falling back to http.
     bool use_alternate_protocols;
+    double alternate_protocol_probability_threshold;
     bool enable_websocket_over_spdy;
 
     bool enable_quic;