Allow unknown fields in corpus parser

As discussed in envoyproxy/envoy#10796, this will allow breaking wire-compatibility changes in the input proto. The pre-existing corpus will still function, but old fields will be ignored.

Risk: Typos in the text proto will cause the fuzzer to run on an incomplete proto. Previously, this would log an error message and skip fuzzing with that test case.

Author: nareddyt

src/text_format.cc

@@ -30,6 +30,7 @@ bool ParseTextMessage(const std::string& data, protobuf::Message* output) {
   TextFormat::Parser parser;
   parser.SetRecursionLimit(100);
   parser.AllowPartialMessage(true);
+  parser.AllowUnknownField(true);
   if (!parser.ParseFromString(data, output)) {
     output->Clear();
     return false;