XHR should respect Cache-Control headers.

As the specification says, XHR should respect Cache-Control headers.
This CL makes ResourceFetcher not to use the Blink-side cache when
a Cache-Control header is set, without understanding its value.

BUG=333804
R=tyoshino

Review URL: https://codereview.chromium.org/144313008

git-svn-id: svn://svn.chromium.org/blink/trunk@165603 bbb929c8-8fbe-4397-9dbb-9b2b20218538