Revert r176393 "Oilpan: Change Persistent<> data members to Member<> in HitTestResult."     https://codereview.chromium.org/326393003/

Reason for revert:
Caused performance regression on Android WebView.
Creating WebHitTestResult with HitTestResult is costly with the CL.

> Oilpan: Change Persistent<> data members to Member<> in HitTestResult.
>
> - Disallow new/delete operations for HitTestResult.
> HitTestResult was used
> -- with new/delete operators
> -- as part objects of ContextMenuController and MouseEventWithHitTestResult.
> -- as stack allocated objects
>
> We'd like to avoid to make such classes in Oilpan.
> So, this CL disallows new/delete, and WebHitTestResult owns another
> class to hold only required data copied from a HitTestResult.
>
> - Move ContextMenuController to Oilpan heap, and trace HitTestResult member.
>
> - Mark MouseEventWithHitTestResults STACK_ALLOCATED.
>
> - We can't get HitTestResult from a WebHitTestResult. So we need to
> introduce new function to WebViewImpl for WebSubstringUtil.mm.
>
> BUG=357163

TBR=aelias@chromium.org,haraken@chromium.org
BUG=395859

Review URL: https://codereview.chromium.org/406413003

git-svn-id: svn://svn.chromium.org/blink/trunk@178743 bbb929c8-8fbe-4397-9dbb-9b2b20218538