Remove kDefaultSupportedQuicVersion in favor of DefaultSupportedQuicVersions()

This change cleans up the codebase and prepares us for using
multiple versions in DefaultSupportedQuicVersions(). Our current
plan is to eventually set it to (h3-29,h3-Q050) if our latest
experiments in Stable go as planned.

R=renjietang@chromium.org

Change-Id: Ie1f6b35b42df07f65a8d800616e8f34427282913
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2419150
Commit-Queue: David Schinazi <dschinazi@chromium.org>
Commit-Queue: Renjie Tang <renjietang@chromium.org>
Auto-Submit: David Schinazi <dschinazi@chromium.org>
Reviewed-by: Renjie Tang <renjietang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#808619}

components/cronet/url_request_context_config_unittest.cc

@@ -448,9 +448,8 @@ TEST(URLRequestContextConfigTest, SetUnsupportedQuicVersion) {
           net::ProxyConfigWithAnnotation::CreateDirect()));
   std::unique_ptr<net::URLRequestContext> context(builder.Build());
   const net::QuicParams* quic_params = context->quic_context()->params();
-  EXPECT_EQ(quic_params->supported_versions.size(), 1u);
-  EXPECT_EQ(quic_params->supported_versions[0],
-            net::kDefaultSupportedQuicVersion);
+  EXPECT_EQ(quic_params->supported_versions,
+            net::DefaultSupportedQuicVersions());
 }
 
 TEST(URLRequestContextConfigTest, SetQuicServerMigrationOptions) {

net/quic/quic_context.h

@@ -12,14 +12,10 @@
 
 namespace net {
 
-// Default QUIC version used in absence of any external configuration.
-constexpr quic::ParsedQuicVersion kDefaultSupportedQuicVersion =
-    quic::ParsedQuicVersion::Q050();
-
-// Returns a list containing only the current default version.
+// Default QUIC supprted versions used in absence of any external configuration.
 inline NET_EXPORT_PRIVATE quic::ParsedQuicVersionVector
 DefaultSupportedQuicVersions() {
-  return quic::ParsedQuicVersionVector{kDefaultSupportedQuicVersion};
+  return quic::ParsedQuicVersionVector{quic::ParsedQuicVersion::Q050()};
 }
 
 // When a connection is idle for 30 seconds it will be closed.

net/url_request/url_request_quic_perftest.cc

@@ -81,7 +81,8 @@ std::unique_ptr<test_server::HttpResponse> HandleRequest(
     const test_server::HttpRequest& request) {
   std::unique_ptr<test_server::BasicHttpResponse> http_response(
       new test_server::BasicHttpResponse());
-  std::string alpn = quic::AlpnForVersion(kDefaultSupportedQuicVersion);
+  std::string alpn =
+      quic::AlpnForVersion(DefaultSupportedQuicVersions().front());
   http_response->AddCustomHeader(
       "Alt-Svc", base::StringPrintf("%s=\"%s:%d\"", alpn.c_str(), kAltSvcHost,
                                     kAltSvcPort));