Revert 167288 "Oilpan: Move core/storage/ to oilpan"

Mixing nullptr and 0 causes a build issue,
since OwnPtr expects nullptr but RawPtr expects 0.

See https://codereview.chromium.org/170183002/ for more details.

> Oilpan: Move core/storage/ to oilpan
> 
> This CL moves Storage and StorageArea to oilpan's heap.
> This CL does not move WebStorageArea to oilpan's heap
> since it's an exposed class to outside Blink.
> Maybe we will move WebStorageArea in the future, but not in this CL.
> 
> BUG=340522
> 
> Review URL: https://codereview.chromium.org/167913004

TBR=haraken@chromium.org

Review URL: https://codereview.chromium.org/169163008

git-svn-id: svn://svn.chromium.org/blink/trunk@167312 bbb929c8-8fbe-4397-9dbb-9b2b20218538