[Hunspell Fuzzer] Restrict fuzzer data to valid UTF8

third_party/hunspell/fuzz/hunspell_fuzzer.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <stddef.h>
 #include <stdint.h>
 #include <string>
 
+#include "base/strings/string16.h"
+#include "base/strings/utf_string_conversions.h"
 #include "third_party/hunspell/src/hunspell/hunspell.hxx"
 #include "third_party/hunspell/fuzz/hunspell_fuzzer_hunspell_dictionary.h"
 
 // Entry point for LibFuzzer.
 extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size) {
   if (!size)
     return 0;
   
   static Hunspell* hunspell = new Hunspell(kHunspellDictionary,
                                            sizeof(kHunspellDictionary));
 
   std::string data_string(reinterpret_cast<const char*>(data), size);
+
+  // hunspell is not handling invalid UTF8. To avoid that, do the same thing
+  // Chromium does - convert to UTF16, and back to UTF8. Valid UTF8 guaranteed.
+  base::string16 utf16_string = base::UTF8ToUTF16(data_string);
+  data_string = base::UTF16ToUTF8(utf16_string);
+
   hunspell->spell(data_string.c_str());
 
   char** suggestions = nullptr;
-  int suggetion_length = hunspell->suggest(&suggestions, data_string.c_str());
-  hunspell->free_list(&suggestions, suggetion_length);
+  int suggestion_length = hunspell->suggest(&suggestions, data_string.c_str());
+  hunspell->free_list(&suggestions, suggestion_length);
 
   return 0;
 }