Load shared proto database in user visible priority

Download DB requires the db to load in this priority and making the
shared one BEST_EFFORT causes delays in downloads.

BUG=1006954

Change-Id: I3154b8f3d782b8367b524063e6def1f0b1d322be
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1839231Reviewed-by: Tommy Nyquist <nyquist@chromium.org>
Reviewed-by: Min Qin <qinmin@chromium.org>
Reviewed-by: Eric Lawrence [MSFT] <ericlaw@microsoft.com>
Commit-Queue: ssid <ssid@chromium.org>
Cr-Commit-Position: refs/heads/master@{#703032}

components/leveldb_proto/internal/shared_proto_database.cc

@@ -60,7 +60,11 @@ SharedProtoDatabase::SharedProtoDatabase(const std::string& client_db_id,
                                          const base::FilePath& db_dir)
     : task_runner_(base::CreateSequencedTaskRunner(
           {base::ThreadPool(), base::MayBlock(),
-           base::TaskPriority::BEST_EFFORT,
+           // crbug/1006954 and crbug/976223 explain why one of the clients
+           // needs run in visible priority. Download DB is always loaded to
+           // check for in progress downloads at startup. So, always load shared
+           // db in USER_VISIBLE priority.
+           base::TaskPriority::USER_VISIBLE,
            base::TaskShutdownBehavior::CONTINUE_ON_SHUTDOWN})),
       db_dir_(db_dir),
       db_(std::make_unique<LevelDB>(client_db_id.c_str())),