Rename WebKit namespace to blink

This code slipped into the tree during the renaming process.

TBR=eseidel@chromium.org
BUG=295096

Review URL: https://codereview.chromium.org/63893002

git-svn-id: svn://svn.chromium.org/blink/trunk@161501 bbb929c8-8fbe-4397-9dbb-9b2b20218538