DEPS: Update leveldatabase from 1.18 to 1.20.

DEPS

 # This file is used to manage the dependencies of the Chromium src repo. It is
 # used by gclient to determine what version of each dependency to check out, and
 # where.
 #
 # For more information, please refer to the official documentation:
 #   https://sites.google.com/a/chromium.org/dev/developers/how-tos/get-the-code
 #
 # When adding a new dependency, please update the top-level .gitignore file
 # to list the dependency's destination directory.
 #
@@ skipping 142 matching lines @@
   'src/third_party/colorama/src':
     Var('chromium_git') + '/external/colorama.git' + '@' + '799604a1041e9b3bc5d2789ecbd7e8db2e18e6b8',
 
   'src/third_party/icu':
     Var('chromium_git') + '/chromium/deps/icu.git' + '@' + '450be73c9ee8ae29d43d4fdc82febb2a5f62bfb5',
 
   'src/third_party/hunspell_dictionaries':
     Var('chromium_git') + '/chromium/deps/hunspell_dictionaries.git' + '@' + 'dc6e7c25bf47cbfb466e0701fd2728b4a12e79d5',
 
   'src/third_party/leveldatabase/src':
-    Var('chromium_git') + '/external/leveldb.git' + '@' + 'a7bff697baa062c8f6b8fb760eacf658712b611a',
+    Var('chromium_git') + '/external/leveldb.git' + '@' + 'a53934a3ae1244679f812d998a4f16f2c7f309a6',
 
   'src/third_party/snappy/src':
     Var('chromium_git') + '/external/snappy.git' + '@' + 'f6a298d7c7ddcfdae824649a61408bcf6b334d92',
 
   'src/tools/gyp':
     Var('chromium_git') + '/external/gyp.git' + '@' + 'e7079f0e0e14108ab0dba58728ff219637458563',
 
   'src/tools/swarming_client':
     Var('chromium_git') + '/external/swarming.client.git' + '@' +  Var('swarming_revision'),
 
@@ skipping 973 matching lines @@
 recursedeps = [
   # buildtools provides clang_format, libc++, and libc++abi
   'src/buildtools',
   # android_tools manages the NDK.
   'src/third_party/android_tools',
   # ANGLE manages DEPS that it also owns the build files for, such as dEQP.
   ("src/third_party/angle", "DEPS.chromium"),
   # SwiftShader manages DEPS that it also owns the build files for, such as Subzero.
   ("src/third_party/swiftshader", "DEPS"),
 ]