It looks like the destructor of DBImpl waits on a condition variable, which is called on a disallowed thread. Backtrace:

base/debug/stack_trace_posix.cc:820
base/debug/stack_trace.cc:203
base/logging.cc:592
base/threading/thread_restrictions.cc:116
base/threading/scoped_blocking_call.cc:112
base/optional.h:70
base/optional.h:683
base/synchronization/condition_variable_posix.cc:70
third_party/leveldatabase/port/port_chromium.cc:40
third_party/leveldatabase/src/db/db_impl.cc:156
third_party/leveldatabase/src/db/db_impl.cc:151
buildtools/third_party/libc++/trunk/include/memory:2325
third_party/leveldatabase/env_chromium.cc:1332
buildtools/third_party/libc++/trunk/include/memory:2325
components/services/leveldb/leveldb_database_impl.cc:67
buildtools/third_party/libc++/trunk/include/memory:2325
mojo/public/cpp/bindings/strong_associated_binding.h:78
mojo/public/cpp/bindings/strong_associated_binding.h:113
base/bind_internal.h:516
base/bind_internal.h:616
base/bind_internal.h:689
base/bind_internal.h:671
base/callback.h:99
mojo/public/cpp/bindings/lib/interface_endpoint_client.cc:332
mojo/public/cpp/bindings/lib/multiplex_router.cc:789
mojo/public/cpp/bindings/lib/multiplex_router.cc:702
mojo/public/cpp/bindings/lib/multiplex_router.cc:611
mojo/public/cpp/bindings/lib/filter_chain.cc:40
mojo/public/cpp/bindings/lib/connector.cc:476
mojo/public/cpp/bindings/lib/connector.cc:505
mojo/public/cpp/bindings/lib/connector.cc:387
mojo/public/cpp/bindings/lib/connector.cc:364
base/bind_internal.h:516
base/bind_internal.h:616
base/bind_internal.h:689
base/bind_internal.h:671
base/callback.h:129
mojo/public/cpp/system/simple_watcher.h:194
base/bind_internal.h:416
base/bind_internal.h:616
base/bind_internal.h:689
base/bind_internal.h:671
base/callback.h:129
mojo/public/cpp/system/simple_watcher.cc:273
base/bind_internal.h:516
base/bind_internal.h:636
base/bind_internal.h:689
base/bind_internal.h:671
base/callback.h:99
base/debug/task_annotator.cc:99
base/task/task_scheduler/task_tracker.cc:641
base/task/task_scheduler/task_tracker_posix.cc:23
base/task/task_scheduler/task_tracker.cc:496
base/task/task_scheduler/scheduler_worker.cc:333
base/task/task_scheduler/scheduler_worker.cc:225
base/task/task_scheduler/scheduler_worker.cc:204
base/threading/platform_thread_posix.cc:81

Check failed: !g_base_sync_primitives_disallowed.Get().Get(). Waiting on a //base sync primitive is not allowed on this thread to prevent jank and deadlock. If waiting on a //base sync primitive is unavoidable, do it within the scope of a ScopedAllowBaseSyncPrimitives. If in a test, use ScopedAllowBaseSyncPrimitivesForTesting.

I'm guessing this isn't very important as it's primarily on shutdown, but the assertion adds to the noise.