Add VersionOfIndex() to quic_protocol.h

net/quic/core/quic_protocol_test.cc

Index: net/quic/core/quic_protocol_test.cc
diff --git a/net/quic/core/quic_protocol_test.cc b/net/quic/core/quic_protocol_test.cc
index 0626bfd055ca365644ce3263eeeedb47ea52437f..48d9fd0a58e4c62dd7f68d7a51aff753d9ed5eb0 100644
--- a/net/quic/core/quic_protocol_test.cc
+++ b/net/quic/core/quic_protocol_test.cc
@@ -314,6 +314,20 @@ TEST(QuicProtocolTest, QuicVersionManager) {
   EXPECT_EQ(QUIC_VERSION_35, manager.GetSupportedVersions()[1]);
 }
 
+TEST(QuicProtocolTest, LookUpVersionByIndex) {
+  QuicVersionVector all_versions = {
+      QUIC_VERSION_30, QUIC_VERSION_31, QUIC_VERSION_32, QUIC_VERSION_33,
+      QUIC_VERSION_34, QUIC_VERSION_35, QUIC_VERSION_36};
+  int version_count = all_versions.size();
+  for (int i = -5; i <= version_count + 1; ++i) {
+    if (i >= 0 && i < version_count) {
+      EXPECT_EQ(all_versions[i], VersionOfIndex(all_versions, i)[0]);
+    } else {
+      EXPECT_EQ(QUIC_VERSION_UNSUPPORTED, VersionOfIndex(all_versions, i)[0]);
+    }
+  }
+}
+
 // Tests that a queue contains the expected data after calls to Add().
 TEST(PacketNumberQueueTest, AddRange) {
   PacketNumberQueue queue;