Make ART engs owners of core/dex_preopt*.mk

Adding ngeoffray@, dbrazdil@, mathewi@ and calin@ to OWNERS for
ART-related makefiles.

Test: N/A
Change-Id: I5952db8336992bd1c32c08bbad85317d0d738d19
diff --git a/core/OWNERS b/core/OWNERS
new file mode 100644
index 0000000..4045061
--- /dev/null
+++ b/core/OWNERS
@@ -0,0 +1,8 @@
+per-file * = ccross@android.com
+per-file * = dwillemsen@google.com
+per-file * = nanzhang@google.com
+
+per-file dex_preopt*.mk = ngeoffray@google.com
+per-file dex_preopt*.mk = calin@google.com
+per-file dex_preopt*.mk = mathewi@google.com
+per-file dex_preopt*.mk = dbrazdil@google.com