Document the fact that leveldb sign warnings aren't getting fixed.

third_party/leveldatabase/BUILD.gn

 # Copyright 2014 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.
 
 import("//testing/test.gni")
 
 defines = [ "LEVELDB_PLATFORM_CHROMIUM=1" ]
 
 config("leveldatabase_config") {
   include_dirs = [
@@ skipping 113 matching lines @@
 
   deps = [
     ":leveldatabase_opts.sse42",
     "//base",
     "//base/third_party/dynamic_annotations",
     "//third_party/re2",
     "//third_party/snappy",
   ]
 
   if (is_win) {
+    # leveldb compiles with a limited set of warnings enabled, and is not
+    # likely to accept fixes for other warnings. See crbug.com/698013
     cflags = [ "/wd4018" ]  # Signed/unsigned mismatch in comparison.
 
     if (is_official_build) {
       # Function recursive on all control paths, crbug.com/620018
       cflags += [ "/wd4717" ]
     }
   }
 }
 
 if (!is_ios && !is_android) {
@@ skipping 54 matching lines @@
   test("leveldb_cache_test") {
     sources = [
       "src/util/cache_test.cc",
     ]
     configs -= [ "//build/config/compiler:chromium_code" ]
     configs += [ "//build/config/compiler:no_chromium_code" ]
     deps = [
       ":leveldb_testutil",
     ]
 
-    # TODO(crbug.com/698013): Fix leveldb to remove the need for suppressing
-    #                         warnings.
     if (is_win) {
       # util\cache_test.cc(167): warning C4018: '<': signed/unsigned mismatch
       # util\cache_test.cc(171): warning C4018: '<': signed/unsigned mismatch
       cflags = [ "/wd4018" ]  # Signed/unsigned mismatch in comparison.
     }
   }
 
   test("leveldb_corruption_test") {
     sources = [
       "src/db/corruption_test.cc",
@@ skipping 171 matching lines @@
       ":leveldb_filename_test",
       ":leveldb_filter_block_test",
       ":leveldb_log_test",
       ":leveldb_skiplist_test",
       ":leveldb_table_test",
       ":leveldb_version_edit_test",
       ":leveldb_write_batch_test",
     ]
   }
 }