Add SetSupportsQuic method to explicitly specify server that supports QUIC.

components/cronet/android/url_request_context_adapter.cc

Index: components/cronet/android/url_request_context_adapter.cc
diff --git a/components/cronet/android/url_request_context_adapter.cc b/components/cronet/android/url_request_context_adapter.cc
index 4552f10118d45760ec9738c9bcd66e99277f4ad6..ac767ec6962cbecb741a58c20c99cf41eebc2c8e 100644
--- a/components/cronet/android/url_request_context_adapter.cc
+++ b/components/cronet/android/url_request_context_adapter.cc
@@ -13,7 +13,7 @@
 #include "net/cert/cert_verifier.h"
 #include "net/http/http_auth_handler_factory.h"
 #include "net/http/http_network_layer.h"
-#include "net/http/http_server_properties_impl.h"
+#include "net/http/http_server_properties.h"
 #include "net/proxy/proxy_config_service_fixed.h"
 #include "net/proxy/proxy_service.h"
 #include "net/ssl/ssl_config_service_defaults.h"
@@ -144,6 +144,34 @@ void URLRequestContextAdapter::InitializeURLRequestContext(
 
   context_.reset(context_builder.Build());
 
+  // Currently (circa M39) enabling QUIC requires setting probability threshold.
+  if (config->enable_quic) {
+    context_->http_server_properties()
+        ->SetAlternateProtocolProbabilityThreshold(1.0f);
+    for (size_t hint = 0; hint < config->quic_hints.size(); ++hint) {
+      const URLRequestContextConfig::QuicHint& quic_hint =
+          *config->quic_hints[hint];
+      net::HostPortPair quic_hint_host(quic_hint.host, quic_hint.port);

[mmenke, 2014/09/16 01:51:38]

optional nit:  Suggest calling this quic_hint_host_port_pair.  Wordier, but we
call them host_port_pair almost everywhere.

[mef, 2014/09/16 08:44:14]

Done.

+      if (quic_hint_host.IsEmpty()) {
+        LOG(ERROR) << "Invalid QUIC hint host: " << quic_hint.host;

[mmenke, 2014/09/16 01:51:38]

This line seems a bit silly, seeing as IsEmpty only returns true if both the
host is the empty string and the port is valid.

[mef, 2014/09/16 08:44:14]

Done.

+        continue;
+      }
+
+      if (quic_hint.alternate_port <= std::numeric_limits<uint16>::min() ||
+          quic_hint.alternate_port > std::numeric_limits<uint16>::max()) {
+        LOG(ERROR) << "Invalid QUIC hint alternate port: "
+                   << quic_hint.alternate_port;
+        continue;
+      }
+
+      context_->http_server_properties()->SetAlternateProtocol(
+          quic_hint_host,
+          static_cast<uint16>(quic_hint.alternate_port),
+          net::AlternateProtocol::QUIC,
+          1.0f);
+    }
+  }
+
   if (VLOG_IS_ON(2)) {
     net_log_observer_.reset(new NetLogObserver());
     context_->net_log()->AddThreadSafeObserver(net_log_observer_.get(),