Replace a DCHECK with a return false, when processing invalid stop waiting data.

net/quic/core/quic_framer.cc

Index: net/quic/core/quic_framer.cc
diff --git a/net/quic/core/quic_framer.cc b/net/quic/core/quic_framer.cc
index 84337191eb72a27daa26fa9f736fcf503d7d8b67..f5d771c361fbb42e9a5ab1b7390a72512873e360 100644
--- a/net/quic/core/quic_framer.cc
+++ b/net/quic/core/quic_framer.cc
@@ -1316,7 +1316,10 @@ bool QuicFramer::ProcessStopWaitingFrame(QuicDataReader* reader,
     set_detailed_error("Unable to read least unacked delta.");
     return false;
   }
-  DCHECK_GE(header.packet_number, least_unacked_delta);
+  if (header.packet_number < least_unacked_delta) {
+    set_detailed_error("Invalid unacked delta.");
+    return false;
+  }
   stop_waiting->least_unacked = header.packet_number - least_unacked_delta;
 
   return true;