Stop calling blink::Platform::current()->cookieJar() in CookieJar.cpp

We no longer have DRT in Blink.

BUG=327256

Review URL: https://codereview.chromium.org/205323004

git-svn-id: svn://svn.chromium.org/blink/trunk@169641 bbb929c8-8fbe-4397-9dbb-9b2b20218538