Use KURL when constructing ResourceRequest

Instead of passing a String url and having ResourceRequest
create a KURL out of it, pass in the readily available
KURL object.

Review URL: https://codereview.chromium.org/561383002

git-svn-id: svn://svn.chromium.org/blink/trunk@181862 bbb929c8-8fbe-4397-9dbb-9b2b20218538