Explicitly construct StringPiece from grease data to avoid msan failure.

gfe-relnote: no behavior change. not protected.
PiperOrigin-RevId: 306491242
Change-Id: Iace5c82eeb1a10636a1d1ab76f567bdf470a52ac

quic/core/crypto/transport_parameters.cc

diff --git a/quic/core/crypto/transport_parameters.cc b/quic/core/crypto/transport_parameters.cc
index 30a9880..6c3f3c5 100644
--- a/quic/core/crypto/transport_parameters.cc
+++ b/quic/core/crypto/transport_parameters.cc
@@ -827,8 +827,9 @@
     char grease_contents[kMaxGreaseLength];
     random->RandBytes(grease_contents, grease_length);
     if (!WriteTransportParameterId(&writer, grease_id, version) ||
-        !WriteTransportParameterStringPiece(&writer, grease_contents,
-                                            version)) {
+        !WriteTransportParameterStringPiece(
+            &writer, quiche::QuicheStringPiece(grease_contents, grease_length),
+            version)) {
       QUIC_BUG << "Failed to write GREASE parameter "
                << TransportParameterIdToString(grease_id);
       return false;