Add Christophe Dumez to core/ OWNERS
Add Christophe Dumez to core/ OWNERS

His nomination was +4ed.

NOTRY=true

Review URL: https://chromiumcodereview.appspot.com/17094018

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@152838 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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