Add owners file for PDFium.

This is currently blocking a PDFium roll in chrome, see
http://build.chromium.org/p/tryserver.chromium.linux/builders/chromium_presubmit/builds/62816/steps/presubmit/logs/stdio

R=thestig@chromium.org

Review URL: https://codereview.chromium.org/1136533003
diff --git a/OWNERS b/OWNERS
new file mode 100644
index 0000000..4b06587
--- /dev/null
+++ b/OWNERS
@@ -0,0 +1,4 @@
+brucedawson@chromium.org
+jam@chromium.org
+thestig@chromium.org
+tsepez@chromium.org