Use std::unique_ptr for CachedResource
https://bugs.webkit.org/show_bug.cgi?id=137736

Reviewed by Darin Adler.

No new tests, no behavior change.

* loader/cache/CachedResource.cpp: Use std::unique_ptr instead of PassOwnPtr|OwnPtr.
(WebCore::CachedResource::removeClient):
* loader/cache/CachedResource.h: Set ctor from private to public.
(WebCore::CachedResource::CachedResourceCallback::schedule):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@174758 268f45cc-cd09-0410-ab3c-d52691b4dbfc