Revert 232620 "Ensure callback objects held by the Indexed DB"

IndexedDBBrowserTestSingleProcess.RenderThreadShutdownTest started to fail
reliably on "XP Tests (dbg)(2)" after this landed:

http://build.chromium.org/p/chromium.win/builders/XP%20Tests%20(dbg)(2)

(look at build 34228 and up)

> Ensure callback objects held by the Indexed DB
> dispatcher are released before WebKit and V8
> are torn down, since the callback objects hold
> V8 handles.
> 
> BUG=308988
> TBR=dgrogan@chromium.org
> 
> Review URL: https://codereview.chromium.org/50333004

TBR=marja@chromium.org

Review URL: https://codereview.chromium.org/57093003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@232649 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 232649