DEPS: Update leveldatabase from 1.18 to 1.20.

BUILD.gn

 # 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.
 
 # This is the root build file for GN. GN will start processing by loading this
 # file, and recursively load all dependencies until all dependencies are either
 # resolved or known not to exist (which will cause the build to fail). So if
 # you add a new build file, there must be some path of dependencies from this
 # file to your new one or GN won't know about it.
 
@@ skipping 756 matching lines @@
       "//components/metrics:serialization",
       "//components/password_manager/content/renderer:browser_tests",
       "//components/rappor:unit_tests",
       "//components/sessions:unit_tests",
       "//media/blink:media_blink_unittests",
       "//media/cast:udp_proxy",
       "//storage/browser:dump_file_system",
       "//third_party/angle:libANGLE",
       "//third_party/angle:libEGL",
       "//third_party/angle:libGLESv2",
-      "//third_party/leveldatabase:leveldb_arena_test",
-      "//third_party/leveldatabase:leveldb_bloom_test",
-      "//third_party/leveldatabase:leveldb_cache_test",
-      "//third_party/leveldatabase:leveldb_corruption_test",
-      "//third_party/leveldatabase:leveldb_crc32c_test",
-      "//third_party/leveldatabase:leveldb_db_bench",
-      "//third_party/leveldatabase:leveldb_db_test",
-      "//third_party/leveldatabase:leveldb_dbformat_test",
-      "//third_party/leveldatabase:leveldb_env_test",
-      "//third_party/leveldatabase:leveldb_filename_test",
-      "//third_party/leveldatabase:leveldb_filter_block_test",
-      "//third_party/leveldatabase:leveldb_log_test",
-      "//third_party/leveldatabase:leveldb_skiplist_test",
-      "//third_party/leveldatabase:leveldb_table_test",
-      "//third_party/leveldatabase:leveldb_version_edit_test",
-      "//third_party/leveldatabase:leveldb_write_batch_test",
+      "//third_party/leveldatabase:leveldb_test_targets",
       "//third_party/libjpeg_turbo:simd",
       "//third_party/opus:opus_compare",
       "//third_party/opus:opus_demo",
       "//third_party/opus:test_opus_api",
       "//third_party/opus:test_opus_decode",
       "//third_party/opus:test_opus_encode",
       "//third_party/opus:test_opus_padding",
       "//third_party/pdfium/third_party:fx_freetype",
       "//third_party/webrtc/system_wrappers:field_trial_default",
       "//third_party/webrtc/system_wrappers:metrics_default",
@@ skipping 305 matching lines @@
   assert(target_name != "")  # Mark as used.
   sources = invoker.actual_sources
   assert(
       sources == invoker.actual_sources,
       "Do not use a platform name in your output directory (found \"$root_build_dir\"). http://crbug.com/548283")
 }
 
 assert_valid_out_dir("_unused") {
   actual_sources = [ "$root_build_dir/foo" ]
 }