Revert 180902 "Move WaitUntilObserver and RespondWithObserver to..."

r180952 fixed crashes caused by r180902.
Now that r180952 was reverted, I need to revert r180902 accordingly.

> Move WaitUntilObserver and RespondWithObserver to Oilpan's heap
> 
> This is a preparation for enabling Oilpan by default for serviceworkers/.
> 
> BUG=340522
> TBR=tkent
> 
> Review URL: https://codereview.chromium.org/467973005

TBR=haraken@chromium.org

Review URL: https://codereview.chromium.org/515523002

git-svn-id: svn://svn.chromium.org/blink/trunk@180975 bbb929c8-8fbe-4397-9dbb-9b2b20218538