Add hnakashima@ to pdf/ and chrome/browser/resources/pdf/ OWNERS

Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I8e870f6ea5bea91a48f09273d7a4d78e44d553b2
Reviewed-on: https://chromium-review.googlesource.com/992853Reviewed-by: dsinclair <dsinclair@chromium.org>
Commit-Queue: dsinclair <dsinclair@chromium.org>
Cr-Commit-Position: refs/heads/master@{#548085}

chrome/browser/resources/pdf/OWNERS

 dsinclair@chromium.org
+hnakashima@chromium.org
 
 # COMPONENT: Internals>Plugins>PDF

pdf/OWNERS

 dsinclair@chromium.org
+hnakashima@chromium.org
 jochen@chromium.org
 thestig@chromium.org