Enable leveldb build in GN world.

third_party/leveldatabase/env_chromium_unittest.cc

 // Copyright (c) 2013 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 "base/file_util.h"
 #include "base/files/file.h"
 #include "base/files/file_enumerator.h"
 #include "base/files/file_path.h"
 #include "base/files/scoped_temp_dir.h"
 #include "base/test/test_suite.h"
@@ skipping 228 matching lines @@
   FILE* f = fopen(new_file_dir.AsUTF8Unsafe().c_str(), "w");
   if (f) {
     fputs("Temp file contents", f);
     fclose(f);
   }
 
   Env* env = IDBEnv();
   std::vector<std::string> result;
   leveldb::Status status = env->GetChildren(dir.AsUTF8Unsafe(), &result);
   EXPECT_TRUE(status.ok());
-  EXPECT_EQ(1, result.size());
+  EXPECT_EQ(1U, result.size());
 
   // And a second time should also return one result
   status = env->GetChildren(dir.AsUTF8Unsafe(), &result);
   EXPECT_TRUE(status.ok());
-  EXPECT_EQ(1, result.size());
+  EXPECT_EQ(1U, result.size());
 }
 
 int main(int argc, char** argv) { return base::TestSuite(argc, argv).Run(); }