Enable HTTP/3 by default for L7XLBs that don't explicitly specify a quicOverride.

Flag is blocked initially, I will unblock it after cl/395525946 is rolled out.

Protected by FLAGS_quic_restart_flag_quic_default_enable_http3_for_gclb.

PiperOrigin-RevId: 396449848

quic/core/quic_version_manager.cc

diff --git a/quic/core/quic_version_manager.cc b/quic/core/quic_version_manager.cc
index 573d6d1..58c0c51 100644
--- a/quic/core/quic_version_manager.cc
+++ b/quic/core/quic_version_manager.cc
@@ -46,6 +46,12 @@
 }
 
 const ParsedQuicVersionVector&
+QuicVersionManager::GetSupportedVersionsWithOnlyHttp3() {
+  MaybeRefilterSupportedVersions();
+  return filtered_supported_versions_with_http3_;
+}
+
+const ParsedQuicVersionVector&
 QuicVersionManager::GetSupportedVersionsWithQuicCrypto() {
   MaybeRefilterSupportedVersions();
   return filtered_supported_versions_with_quic_crypto_;
@@ -86,6 +92,7 @@
 void QuicVersionManager::RefilterSupportedVersions() {
   filtered_supported_versions_ =
       FilterSupportedVersions(allowed_supported_versions_);
+  filtered_supported_versions_with_http3_.clear();
   filtered_supported_versions_with_quic_crypto_.clear();
   filtered_transport_versions_.clear();
   filtered_supported_alpns_.clear();
@@ -96,6 +103,9 @@
                   transport_version) == filtered_transport_versions_.end()) {
       filtered_transport_versions_.push_back(transport_version);
     }
+    if (version.UsesHttp3()) {
+      filtered_supported_versions_with_http3_.push_back(version);
+    }
     if (version.handshake_protocol == PROTOCOL_QUIC_CRYPTO) {
       filtered_supported_versions_with_quic_crypto_.push_back(version);
     }

quic/core/quic_version_manager.h

diff --git a/quic/core/quic_version_manager.h b/quic/core/quic_version_manager.h
index 487d057..501ecc5 100644
--- a/quic/core/quic_version_manager.h
+++ b/quic/core/quic_version_manager.h
@@ -22,6 +22,9 @@
   // as the versions passed to the constructor.
   const ParsedQuicVersionVector& GetSupportedVersions();
 
+  // Returns currently supported versions using HTTP/3.
+  const ParsedQuicVersionVector& GetSupportedVersionsWithOnlyHttp3();
+
   // Returns currently supported versions using QUIC crypto.
   const ParsedQuicVersionVector& GetSupportedVersionsWithQuicCrypto();
 
@@ -83,6 +86,8 @@
   // This vector contains QUIC versions which are currently supported based on
   // flags.
   ParsedQuicVersionVector filtered_supported_versions_;
+  // Currently supported versions using HTTP/3.
+  ParsedQuicVersionVector filtered_supported_versions_with_http3_;
   // Currently supported versions using QUIC crypto.
   ParsedQuicVersionVector filtered_supported_versions_with_quic_crypto_;
   // This vector contains the transport versions from

quic/core/quic_version_manager_test.cc

diff --git a/quic/core/quic_version_manager_test.cc b/quic/core/quic_version_manager_test.cc
index 5776b39..75ceed4 100644
--- a/quic/core/quic_version_manager_test.cc
+++ b/quic/core/quic_version_manager_test.cc
@@ -37,6 +37,7 @@
 
   EXPECT_EQ(FilterSupportedVersions(AllSupportedVersions()),
             manager.GetSupportedVersions());
+  EXPECT_TRUE(manager.GetSupportedVersionsWithOnlyHttp3().empty());
   EXPECT_EQ(CurrentSupportedVersionsWithQuicCrypto(),
             manager.GetSupportedVersionsWithQuicCrypto());
   EXPECT_THAT(manager.GetSupportedAlpns(),
@@ -51,6 +52,9 @@
             manager.GetSupportedVersionsWithQuicCrypto().size());
   EXPECT_EQ(FilterSupportedVersions(AllSupportedVersions()),
             manager.GetSupportedVersions());
+  EXPECT_EQ(1u, manager.GetSupportedVersionsWithOnlyHttp3().size());
+  EXPECT_EQ(CurrentSupportedHttp3Versions(),
+            manager.GetSupportedVersionsWithOnlyHttp3());
   EXPECT_EQ(CurrentSupportedVersionsWithQuicCrypto(),
             manager.GetSupportedVersionsWithQuicCrypto());
   EXPECT_THAT(manager.GetSupportedAlpns(),
@@ -65,6 +69,9 @@
             manager.GetSupportedVersionsWithQuicCrypto().size());
   EXPECT_EQ(FilterSupportedVersions(AllSupportedVersions()),
             manager.GetSupportedVersions());
+  EXPECT_EQ(1u, manager.GetSupportedVersionsWithOnlyHttp3().size());
+  EXPECT_EQ(CurrentSupportedHttp3Versions(),
+            manager.GetSupportedVersionsWithOnlyHttp3());
   EXPECT_EQ(CurrentSupportedVersionsWithQuicCrypto(),
             manager.GetSupportedVersionsWithQuicCrypto());
   EXPECT_THAT(manager.GetSupportedAlpns(),