Revert of Remove obsolete QUIC disabling code.

net/quic/chromium/quic_chromium_client_session.h

Index: net/quic/chromium/quic_chromium_client_session.h
diff --git a/net/quic/chromium/quic_chromium_client_session.h b/net/quic/chromium/quic_chromium_client_session.h
index dcf436381f69a1cfa4bfa0f3b8435e178f1ecb7f..5a2ac65315aceb3458f0c6dcb478cbb808526410 100644
--- a/net/quic/chromium/quic_chromium_client_session.h
+++ b/net/quic/chromium/quic_chromium_client_session.h
@@ -58,6 +58,18 @@
       public QuicChromiumPacketReader::Visitor,
       public QuicChromiumPacketWriter::WriteErrorObserver {
  public:
+  // Reasons to disable QUIC, that is under certain pathological
+  // connection errors.  Note: these values must be kept in sync with
+  // the corresponding values of QuicDisabledReason in:
+  // tools/metrics/histograms/histograms.xml
+  enum QuicDisabledReason {
+    QUIC_DISABLED_NOT = 0,  // default, not disabled
+    QUIC_DISABLED_PUBLIC_RESET_POST_HANDSHAKE = 1,
+    QUIC_DISABLED_TIMEOUT_WITH_OPEN_STREAMS = 2,
+    QUIC_DISABLED_BAD_PACKET_LOSS_RATE = 3,
+    QUIC_DISABLED_MAX = 4,
+  };
+
   // An interface for observing events on a session.
   class NET_EXPORT_PRIVATE Observer {
    public:
@@ -236,6 +248,8 @@
   bool CanPool(const std::string& hostname, PrivacyMode privacy_mode) const;
 
   const QuicServerId& server_id() const { return server_id_; }
+
+  QuicDisabledReason disabled_reason() const { return disabled_reason_; }
 
   // Migrates session onto new socket, i.e., starts reading from
   // |socket| in addition to any previous sockets, and sets |writer|
@@ -344,6 +358,7 @@
   bool going_away_;
   // True when the session receives a go away from server due to port migration.
   bool port_migration_detected_;
+  QuicDisabledReason disabled_reason_;
   TokenBindingSignatureMap token_binding_signatures_;
   // UMA histogram counters for streams pushed to this session.
   int streams_pushed_count_;