Allow base::DoNothing inside Blink.

Bug: None
Change-Id: I98eeaff0d8de99074c6c3823bfcbe6a16ce0506b
Reviewed-on: https://chromium-review.googlesource.com/1012109Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Mounir Lamouri <mlamouri@chromium.org>
Cr-Commit-Position: refs/heads/master@{#550994}

third_party/blink/tools/audit_non_blink_usage.py

@@ -51,6 +51,9 @@ _CONFIG = [
             'base::span',
             'logging::GetVlogLevel',
 
+            # //base/bind_helpers.h.
+            'base::DoNothing',
+
             # //base/callback.h is allowed, but you need to use WTF::Bind or
             # WTF::BindRepeating to create callbacks in Blink.
             'base::OnceCallback',