gfe-relnote: Change a string to a char[16] to avoid using data() in string, which is sometimes const.  Fixes a Chrome merge failure of cr/305944808.  Protected by existing flags gfe2_reloadable_flag_quic_enable_version_draft_25_v3 and gfe2_reloadable_flag_quic_enable_version_draft_27.

Non-const data() on string is available in C++17.

PiperOrigin-RevId: 306270586
Change-Id: I15a42c3928bb413dbc1ab3a2adde2f5a339df027

quic/core/crypto/transport_parameters.cc

diff --git a/quic/core/crypto/transport_parameters.cc b/quic/core/crypto/transport_parameters.cc
index 9cd98e7..30a9880 100644
--- a/quic/core/crypto/transport_parameters.cc
+++ b/quic/core/crypto/transport_parameters.cc
@@ -821,9 +821,11 @@
         << grease_id64 << " invalid for " << version;
     TransportParameters::TransportParameterId grease_id =
         static_cast<TransportParameters::TransportParameterId>(grease_id64);
-    size_t grease_length = random->RandUint64() % 16;
-    std::string grease_contents(grease_length, '\0');
-    random->RandBytes(grease_contents.data(), grease_contents.size());
+    const size_t kMaxGreaseLength = 16;
+    const size_t grease_length = random->RandUint64() % kMaxGreaseLength;
+    DCHECK_GE(kMaxGreaseLength, grease_length);
+    char grease_contents[kMaxGreaseLength];
+    random->RandBytes(grease_contents, grease_length);
     if (!WriteTransportParameterId(&writer, grease_id, version) ||
         !WriteTransportParameterStringPiece(&writer, grease_contents,
                                             version)) {