Revert "Change NetworkSessionConfigurator to process multiple versions from quic_version field"

This reverts commit 4721652f.

Reason for revert: https://crbug.com/689762#c12

Original change's description:
> Change NetworkSessionConfigurator to process multiple versions from quic_version field
> 
> Bug: 689762
> Change-Id: Ic0de2dacd01158d85318794d05f8f763659d9228
> Reviewed-on: https://chromium-review.googlesource.com/565784
> Commit-Queue: Zhongyi Shi <zhongyi@chromium.org>
> Reviewed-by: Ryan Hamilton <rch@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#485678}

TBR=rch@chromium.org,zhongyi@chromium.org

Change-Id: If18efa529febe19aa543eb2b6947434daeed7374
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 689762
Reviewed-on: https://chromium-review.googlesource.com/567283Reviewed-by: Mark Mentovai <mark@chromium.org>
Commit-Queue: Mark Mentovai <mark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#485940}

components/network_session_configurator/browser/network_session_configurator.cc

@@ -233,9 +233,8 @@ size_t GetQuicMaxPacketLength(const VariationParameters& quic_trial_params) {
   return 0;
 }
 
-net::QuicVersionVector GetQuicVersions(
-    const VariationParameters& quic_trial_params) {
-  return network_session_configurator::ParseQuicVersions(
+net::QuicVersion GetQuicVersion(const VariationParameters& quic_trial_params) {
+  return network_session_configurator::ParseQuicVersion(
       GetVariationParam(quic_trial_params, "quic_version"));
 }
 
@@ -307,35 +306,28 @@ void ConfigureQuicParams(base::StringPiece quic_trial_group,
 
   params->quic_user_agent_id = quic_user_agent_id;
 
-  net::QuicVersionVector supported_versions =
-      GetQuicVersions(quic_trial_params);
-  if (!supported_versions.empty())
+  net::QuicVersion version = GetQuicVersion(quic_trial_params);
+  if (version != net::QUIC_VERSION_UNSUPPORTED) {
+    net::QuicVersionVector supported_versions;
+    supported_versions.push_back(version);
     params->quic_supported_versions = supported_versions;
+  }
 }
 
 }  // anonymous namespace
 
 namespace network_session_configurator {
 
-net::QuicVersionVector ParseQuicVersions(const std::string& quic_versions) {
-  net::QuicVersionVector supported_versions;
-  net::QuicVersionVector all_supported_versions = net::AllSupportedVersions();
-
-  for (const base::StringPiece& version : base::SplitStringPiece(
-           quic_versions, ",", base::TRIM_WHITESPACE, base::SPLIT_WANT_ALL)) {
-    auto it = all_supported_versions.begin();
-    while (it != all_supported_versions.end()) {
-      if (net::QuicVersionToString(*it) == version) {
-        supported_versions.push_back(*it);
-        // Remove the supported version to deduplicate versions extracted from
-        // |quic_versions|.
-        all_supported_versions.erase(it);
-        continue;
-      }
-      it++;
+net::QuicVersion ParseQuicVersion(const std::string& quic_version) {
+  net::QuicVersionVector supported_versions = net::AllSupportedVersions();
+  for (size_t i = 0; i < supported_versions.size(); ++i) {
+    net::QuicVersion version = supported_versions[i];
+    if (net::QuicVersionToString(version) == quic_version) {
+      return version;
     }
   }
-  return supported_versions;
+
+  return net::QUIC_VERSION_UNSUPPORTED;
 }
 
 void ParseCommandLineAndFieldTrials(const base::CommandLine& command_line,
@@ -386,11 +378,13 @@ void ParseCommandLineAndFieldTrials(const base::CommandLine& command_line,
     }
 
     if (command_line.HasSwitch(switches::kQuicVersion)) {
-      net::QuicVersionVector supported_versions =
-          network_session_configurator::ParseQuicVersions(
-              command_line.GetSwitchValueASCII(switches::kQuicVersion));
-      if (!supported_versions.empty())
+      net::QuicVersion version = network_session_configurator::ParseQuicVersion(
+          command_line.GetSwitchValueASCII(switches::kQuicVersion));
+      if (version != net::QUIC_VERSION_UNSUPPORTED) {
+        net::QuicVersionVector supported_versions;
+        supported_versions.push_back(version);
         params->quic_supported_versions = supported_versions;
+      }
     }
 
     if (command_line.HasSwitch(switches::kOriginToForceQuicOn)) {

components/network_session_configurator/browser/network_session_configurator.h

@@ -18,8 +18,9 @@ namespace network_session_configurator {
 // Helper functions to configure HttpNetworkSession::Params based on field
 // trials and command line.
 
-// Parse serialized QUIC versions string.
-net::QuicVersionVector ParseQuicVersions(const std::string& quic_versions);
+// Parse serialized QUIC version string.
+// Return QUIC_VERSION_UNSUPPORTED on failure.
+net::QuicVersion ParseQuicVersion(const std::string& quic_version);
 
 // Configure |params| based on field trials and command line,
 // and forcing (policy or other command line) arguments.

components/network_session_configurator/browser/network_session_configurator_unittest.cc

@@ -305,42 +305,6 @@ TEST_F(NetworkSessionConfiguratorTest, QuicVersionFromFieldTrialParams) {
   EXPECT_EQ(supported_versions, params_.quic_supported_versions);
 }
 
-TEST_F(NetworkSessionConfiguratorTest,
-       MultipleQuicVersionFromFieldTrialParams) {
-  std::map<std::string, std::string> field_trial_params;
-  std::string quic_versions =
-      net::QuicVersionToString(net::AllSupportedVersions().front()) + "," +
-      net::QuicVersionToString(net::AllSupportedVersions().back());
-
-  field_trial_params["quic_version"] = quic_versions;
-  variations::AssociateVariationParams("QUIC", "Enabled", field_trial_params);
-  base::FieldTrialList::CreateFieldTrial("QUIC", "Enabled");
-
-  ParseFieldTrials();
-
-  net::QuicVersionVector supported_versions;
-  supported_versions.push_back(net::AllSupportedVersions().front());
-  supported_versions.push_back(net::AllSupportedVersions().back());
-  EXPECT_EQ(supported_versions, params_.quic_supported_versions);
-}
-
-TEST_F(NetworkSessionConfiguratorTest, SameQuicVersionsFromFieldTrialParams) {
-  std::map<std::string, std::string> field_trial_params;
-  std::string quic_versions =
-      net::QuicVersionToString(net::AllSupportedVersions().front()) + "," +
-      net::QuicVersionToString(net::AllSupportedVersions().front());
-
-  field_trial_params["quic_version"] = quic_versions;
-  variations::AssociateVariationParams("QUIC", "Enabled", field_trial_params);
-  base::FieldTrialList::CreateFieldTrial("QUIC", "Enabled");
-
-  ParseFieldTrials();
-
-  net::QuicVersionVector supported_versions;
-  supported_versions.push_back(net::AllSupportedVersions().front());
-  EXPECT_EQ(supported_versions, params_.quic_supported_versions);
-}
-
 TEST_F(NetworkSessionConfiguratorTest,
        QuicConnectionOptionsFromFieldTrialParams) {
   std::map<std::string, std::string> field_trial_params;