[clang-tidy] Add flowerhack@ to clang-tidy OWNERS.

I've been going through the rather-bitrotted set of requests for new
clang-tidy checks that have accumulated over the years. The security
team, in particular, is interested in seeing how these checks improve
our overall security posture.

Since this involves some of the first substantial clang-tidy changes to
our config in a while, I'd like to make it easy for me to respond if a
tidy check should suddenly need to be disabled or cause a problem in
some way, and

I looked at the documentation on OWNERS but it was unclear to me whether
the correct form was to have two separate "per-file" directives, or if
it's possible to append one's username to the end of a per-file
directive.  I went with the former but can change to the latter if
that's correct; wasn't sure how to "test" an OWNERS change.

Change-Id: Ic91fe7d1722b08e50f7a3e6a9572734d99c62dd0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6527209
Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Julia Hansbrough <flowerhack@google.com>
Reviewed-by: Rick Byers <rbyers@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1458363}

OWNERS

@@ -7,6 +7,7 @@ file://ATL_OWNERS
 
 per-file .clang-format=thakis@chromium.org
 per-file .clang-tidy=file://styleguide/c++/OWNERS
+per-file .clang-tidy=flowerhack@google.com
 per-file .clangd=file://styleguide/c++/OWNERS
 per-file .gitattributes=*
 per-file .gitignore=*