CODE_OWNERS: Add owners for the corelibs overlays.

- Tony P. owns the Foundation overlay.
- Daniel S. owns the Dispatch overlay.
- Brian C. owns the XCTest overlay.

(A reminder that ownership of the component does not mean they are the
only qualified reviewer for that component, nor does it necessarily
mean they are the head of the corresponding team at Apple)

CODE_OWNERS.TXT

@@ -12,6 +12,11 @@ E: ben_cohen@apple.com
 G: airspeedswift
 D: Swift standard library
 
+N: Brian Croom
+E: bcroom@apple.com
+G: briancroom
+D: XCTest overlay
+
 N: Erik Eckstein
 E: eeckstein@apple.com
 G: eeckstein
@@ -47,6 +52,11 @@ E: rjmccall@apple.com
 G: rjmccall
 D: Demangler, IRGen, Runtime
 
+N: Tony Parker
+E: anthony.parker@apple.com
+G: parkera
+D: Foundation overlay
+
 N: Slava Pestov
 E: spestov@apple.com
 G: slavapestov
@@ -57,6 +67,11 @@ E: jordan_rose@apple.com
 G: jrose-apple
 D: ClangImporter, Serialization, PrintAsObjC, Driver, Frontend
 
+N: Daniel Steffen
+E: dsteffen@apple.com
+G: das
+D: Dispatch overlay
+
 N: Anna Zaks
 E: ganna@apple.com
 G: AnnaZaks