Fix a reference to webkit_chromium_resources.pak.

This was found by Linux ChromeOS Release build on Chromium when
CL https://codereview.chromium.org/19537010/ landed (even with all trybots green).

I missed it on Blink because I grepped only for WebKit.grd which found zero
entries, but not for webkit_chromium.

R=abarth@chromium.org

Review URL: https://chromiumcodereview.appspot.com/20342002

git-svn-id: svn://svn.chromium.org/blink/trunk@155178 bbb929c8-8fbe-4397-9dbb-9b2b20218538