Add a new priority level, THROTTLED, below IDLE.

net/quic/quic_http_utils.cc

Index: net/quic/quic_http_utils.cc
diff --git a/net/quic/quic_http_utils.cc b/net/quic/quic_http_utils.cc
index c6dd505f2c64a6ca10cdbf7e2c516f2cf68cdbe6..e3b626315d6df26785af93f3d7d72c23ca4dd077 100644
--- a/net/quic/quic_http_utils.cc
+++ b/net/quic/quic_http_utils.cc
@@ -12,14 +12,18 @@ SpdyPriority ConvertRequestPriorityToQuicPriority(
     const RequestPriority priority) {
   DCHECK_GE(priority, MINIMUM_PRIORITY);
   DCHECK_LE(priority, MAXIMUM_PRIORITY);
-  return static_cast<SpdyPriority>(HIGHEST - priority);
+  return static_cast<SpdyPriority>(MAXIMUM_PRIORITY - priority +
+                                   kV3HighestPriority);
 }
 
 NET_EXPORT_PRIVATE RequestPriority
 ConvertQuicPriorityToRequestPriority(SpdyPriority priority) {
   // Handle invalid values gracefully.
-  return (priority >= 5) ? IDLE
-                         : static_cast<RequestPriority>(HIGHEST - priority);
+  return ((priority - kV3HighestPriority) >
+                  (MAXIMUM_PRIORITY - MINIMUM_PRIORITY)
+              ? IDLE
+              : static_cast<RequestPriority>(MAXIMUM_PRIORITY -
+                                             (priority - kV3HighestPriority)));
 }
 
 std::unique_ptr<base::Value> QuicRequestNetLogCallback(