Revert of Oilpan: Prepare to move XPath::NodeSet, XPath::ValueData, and XPath::Value to Oilpan heap. (https://codereview.chromium.org/291763002/)

Reason for revert:
It caused crashes on Oilpan perf bot.

BUG=374814


Original issue's description:
> Oilpan: Prepare to move XPath::NodeSet, XPath::ValueData, and XPath::Value to Oilpan heap.
> 
> Note:
> - XPath::Value is a part object of XPathResult.
> - XPath::NodeSet was a part object of XPathResult or XPath::ValueData, and
>   NodeSet is also used as an independent object. This CL makes NodeSet not a
>   part object because using GarbageCollected object as a part object is
>   dangerous.
> 
> This is a preparation to remove RefPtr<Attr> and RefPtr<Node>.
> 
> BUG=357163,373814
> R=haraken@chromium.org
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=174239

TBR=oilpan-reviews@chromium.org,haraken@chromium.org,ager@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=357163,373814

Review URL: https://codereview.chromium.org/299523002

git-svn-id: svn://svn.chromium.org/blink/trunk@174316 bbb929c8-8fbe-4397-9dbb-9b2b20218538