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.cc b/net/http/http_network_session.cc
index ff178da..43153f7 100644
--- a/net/http/http_network_session.cc
+++ b/net/http/http_network_session.cc
@@ -81,6 +81,7 @@
       force_spdy_over_ssl(true),
       force_spdy_always(false),
       use_alternate_protocols(false),
+      alternate_protocol_probability_threshold(0),
       enable_websocket_over_spdy(false),
       enable_quic(false),
       enable_quic_port_selection(true),
@@ -182,6 +183,9 @@
   if (HpackHuffmanAggregator::UseAggregator()) {
     huffman_aggregator_.reset(new HpackHuffmanAggregator());
   }
+
+  http_server_properties_->SetAlternateProtocolProbabilityThreshold(
+      params.alternate_protocol_probability_threshold);
 }
 
 HttpNetworkSession::~HttpNetworkSession() {