Add kjellander@webrtc.org to more BUILD.gn OWNERS files.

NOTRY=True

Review-Url: https://codereview.webrtc.org/2258983003
Cr-Commit-Position: refs/heads/master@{#13826}
diff --git a/webrtc/sdk/OWNERS b/webrtc/sdk/OWNERS
index cd06158..2a11291 100644
--- a/webrtc/sdk/OWNERS
+++ b/webrtc/sdk/OWNERS
@@ -1 +1,8 @@
 tkchin@webrtc.org
+
+# These are for the common case of adding or renaming files. If you're doing
+# structural changes, please get a review from a reviewer in this file.
+per-file *.gyp=*
+per-file *.gypi=*
+
+per-file BUILD.gn=kjellander@webrtc.org