Add build/fuchsia/OWNERS and use it in wildcards in some OWNERS files.

As more of Chromium is ported to Fuchsia, per-directory OWNERS files can
link back to the master build/fuchsia/OWNERS to manage Fuchsia-specific
file ownership more easily.

Change-Id: Ic8cc48b681b361fc280c793a0361aebefea860cd
Reviewed-on: https://chromium-review.googlesource.com/569501
Commit-Queue: Wez <wez@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Reviewed-by: danakj <danakj@chromium.org>
Cr-Commit-Position: refs/heads/master@{#486576}

diff --git a/base/OWNERS b/base/OWNERS
index 28043c42..51da1f5 100644
--- a/base/OWNERS
+++ b/base/OWNERS

@@ -32,6 +32,9 @@
 per-file *android*=file://base/android/OWNERS
 per-file BUILD.gn=file://base/android/OWNERS
 
+# For Fuchsia-specific changes:
+per-file *_fuchsia*=file://build/fuchsia/OWNERS
+
 # For FeatureList API:
 per-file feature_list*=asvitkine@chromium.org
 per-file feature_list*=isherman@chromium.org