Roll protobuf to v31.0

R=sophiechang@chromium.org

Bug: 417774625
NO_IFTTT=This is a protobuf roll, and we do not use the relevant files.
Cq-Include-Trybots: luci.chromium.try:chromeos-amd64-generic-cfi-thin-lto-rel,linux_chromium_cfi_rel_ng;luci.chrome.try:chromeos-arm-generic-cfi-thin-lto-chrome,chromeos-arm64-generic-cfi-thin-lto-chrome,chromeos-betty-cfi-thin-lto-chrome

Change-Id: I3d05526b3b18b7aa6a49a8c488b9b375841177be
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6549497
Commit-Queue: Tommy Nyquist <nyquist@chromium.org>
Reviewed-by: Danil Chapovalov <danilchap@chromium.org>
Reviewed-by: Sophie Chang <sophiechang@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1463751}
NOKEYCHECK=True
GitOrigin-RevId: d893a0c472cca445542a833bbb475ca5ac9e2556

BUILD.gn

diff --git a/BUILD.gn b/BUILD.gn
index 3bd2ea4..896b9de 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -102,6 +102,7 @@
     "//third_party/abseil-cpp/absl/status",
     "//third_party/abseil-cpp/absl/status:statusor",
     "//third_party/abseil-cpp/absl/strings",
+    "//third_party/abseil-cpp/absl/strings:charset",
     "//third_party/abseil-cpp/absl/strings:cord",
     "//third_party/abseil-cpp/absl/strings:has_ostream_operator",
     "//third_party/abseil-cpp/absl/strings:str_format",