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

third_party/leveldatabase/env_chromium.h

Index: third_party/leveldatabase/env_chromium.h
diff --git a/third_party/leveldatabase/env_chromium.h b/third_party/leveldatabase/env_chromium.h
index 690a032ad763cd96946e633de5145322bff4a592..9539ef13cf34208cf68e46d85ec0d52d1d5dc2a1 100644
--- a/third_party/leveldatabase/env_chromium.h
+++ b/third_party/leveldatabase/env_chromium.h
@@ -242,6 +242,13 @@ class DBTracker {
   // DBTracker singleton instance.
   static DBTracker* GetInstance();
 
+  // Returns name of memory-infra dump for |tracked_db|. Can be used to attach
+  // additional info to the database dump, or to properly attribute memory
+  // usage in memory dump providers that also dump |tracked_db|.
+  // Note that |tracked_db| should be a live database instance produced by
+  // OpenDatabase() method or leveldb_env::OpenDB() function.
+  static std::string GetMemoryDumpName(leveldb::DB* tracked_db);
+
   // Provides extra information about a tracked database.
   class TrackedDB : public leveldb::DB {
    public:
@@ -252,6 +259,9 @@ class DBTracker {
   // Opens a database and starts tracking it. As long as the opened database
   // is alive (i.e. its instance is not destroyed) the database is exposed to
   // memory-infra and is enumerated by VisitDatabases() method.

[pwnall, 2017/07/07 22:30:29]

nit 1:  Can you please add a statement that this is an implementation detail,
and other modules should call leveldb_env::OpenDB()?

+  // The function guarantees that:

[pwnall, 2017/07/07 22:30:29]

nit 2: You could say that the function has the same guarantees as
leveldb_env::OpenDB(). I think a redirect is acceptable here, as this is an
implementation detail, and most readers should end up reading
leveldb_env::OpenDB() instead. Also, the redirect is a reminder that OpenDB()
relies on OpenDatabase() for these guarantees.

[DmitrySkiba, 2017/07/17 22:09:25]

Done.

+  //   1. |dbptr| is not touched on failure
+  //   2. |dbptr| is not NULL on success
   leveldb::Status OpenDatabase(const leveldb::Options& options,
                                const std::string& name,
                                TrackedDB** dbptr);
@@ -285,7 +295,9 @@ class DBTracker {
 };
 
 // Opens a database and exposes it to Chrome's tracing (see DBTracker for
-// details). Note that |dbptr| is touched only when function succeeds.
+// details). The function guarantees that:
+//   1. |dbptr| is not touched on failure
+//   2. |dbptr| is not NULL on success
 leveldb::Status OpenDB(const leveldb::Options& options,
                        const std::string& name,
                        std::unique_ptr<leveldb::DB>* dbptr);