Add component to owners

Add the component marker to the PDFium OWNERS file to help identify the
right crbug label.

Bug: chromium:761018
Change-Id: I50fb66f57efbc50de2eedaeb9786d840ca3e78a3
Reviewed-on: https://pdfium-review.googlesource.com/12712
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Commit-Queue: dsinclair <dsinclair@chromium.org>
diff --git a/OWNERS b/OWNERS
index 37876c5..ea8e2db 100644
--- a/OWNERS
+++ b/OWNERS
@@ -11,3 +11,5 @@
 
 # For Skia related changes
 caryclark@google.com
+
+# COMPONENT: Internals>Plugins>PDF