Add a new migration cause: network connected post path degrading.

This separates cases out from connection migration on path degrading
and helps collect data on how often a new network is connected after
path degrading is detected.

Change-Id: I36dc7306d6b94c84a85ffceb61a91645b312650f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1888952
Auto-Submit: Zhongyi Shi <zhongyi@chromium.org>
Reviewed-by: Ryan Hamilton <rch@chromium.org>
Commit-Queue: Ryan Hamilton <rch@chromium.org>
Cr-Commit-Position: refs/heads/master@{#710805}

net/quic/quic_chromium_client_session.cc

@@ -209,6 +209,8 @@ std::string MigrationCauseToString(MigrationCause cause) {
       return "OnPathDegrading";
     case CHANGE_PORT_ON_PATH_DEGRADING:
       return "ChangePortOnPathDegrading";
+    case NEW_NETWORK_CONNECTED_POST_PATH_DEGRADING:
+      return "NewNetworkConnectedPostPathDegrading";
     default:
       QUIC_NOTREACHED();
       break;
@@ -2083,7 +2085,7 @@ void QuicChromiumClientSession::OnNetworkConnected(
     return;
 
   if (connection()->IsPathDegrading()) {
-    current_migration_cause_ = CHANGE_NETWORK_ON_PATH_DEGRADING;
+    current_migration_cause_ = NEW_NETWORK_CONNECTED_POST_PATH_DEGRADING;
   }
 
   if (wait_for_new_network_) {

net/quic/quic_chromium_client_session.h

@@ -89,13 +89,14 @@ enum class ConnectionMigrationMode {
 // Cause of a migration.
 enum MigrationCause {
   UNKNOWN_CAUSE,
-  ON_NETWORK_CONNECTED,                // No probing.
-  ON_NETWORK_DISCONNECTED,             // No probing.
-  ON_WRITE_ERROR,                      // No probing.
-  ON_NETWORK_MADE_DEFAULT,             // With probing.
-  ON_MIGRATE_BACK_TO_DEFAULT_NETWORK,  // With probing.
-  CHANGE_NETWORK_ON_PATH_DEGRADING,    // With probing.
-  CHANGE_PORT_ON_PATH_DEGRADING,       // With probing.
+  ON_NETWORK_CONNECTED,                       // No probing.
+  ON_NETWORK_DISCONNECTED,                    // No probing.
+  ON_WRITE_ERROR,                             // No probing.
+  ON_NETWORK_MADE_DEFAULT,                    // With probing.
+  ON_MIGRATE_BACK_TO_DEFAULT_NETWORK,         // With probing.
+  CHANGE_NETWORK_ON_PATH_DEGRADING,           // With probing.
+  CHANGE_PORT_ON_PATH_DEGRADING,              // With probing.
+  NEW_NETWORK_CONNECTED_POST_PATH_DEGRADING,  // With probing.
   MIGRATION_CAUSE_MAX
 };