Use leveldb_env::OpenDB() to open leveldb databases.

PRESUBMIT.py

 # Copyright (c) 2012 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.
 
 """Top-level presubmit script for Chromium.
 
 See http://dev.chromium.org/developers/how-tos/depottools/presubmit-scripts
 for more details about the presubmit API built into depot_tools.
 """
 
@@ skipping 366 matching lines @@
         'AllowJavascript(), OnJavascriptAllowed()/OnJavascriptDisallowed(),',
         'and CallJavascriptFunction(). See https://goo.gl/qivavq.',
       ),
       False,
       (
         r'^content[\\\/]browser[\\\/]webui[\\\/]web_ui_impl\.(cc|h)$',
         r'^content[\\\/]public[\\\/]browser[\\\/]web_ui\.h$',
         r'^content[\\\/]public[\\\/]test[\\\/]test_web_ui\.(cc|h)$',
       ),
     ),
+    (
+      'leveldb::DB::Open',
+      (
+        'Instead of leveldb::DB::Open() use leveldb_env::OpenDB() from',
+        'third_party/leveldatabase/env_chromium.h. It exposes databases to',
+        "Chrome's tracing, making their memory usage visible.",
+      ),
+      True,
+      (
+        r'^third_party/leveldatabase/.*\.(cc|h)$',
+      ),
+    )
 )
 
 
 _IPC_ENUM_TRAITS_DEPRECATED = (
     'You are using IPC_ENUM_TRAITS() in your code. It has been deprecated.\n'
     'See http://www.chromium.org/Home/chromium-security/education/security-tips-for-ipc')
 
 
 _VALID_OS_MACROS = (
     # Please keep sorted.
@@ skipping 2015 matching lines @@
       output_api,
       json_url='http://chromium-status.appspot.com/current?format=json'))
 
   results.extend(
       input_api.canned_checks.CheckPatchFormatted(input_api, output_api))
   results.extend(input_api.canned_checks.CheckChangeHasBugField(
       input_api, output_api))
   results.extend(input_api.canned_checks.CheckChangeHasDescription(
       input_api, output_api))
   return results