Revert 273547 "Reset scoped_ptr to make plugin crash before ente..."

Revert 273547 "Reset scoped_ptr to make plugin crash before ente..."

> Reset scoped_ptr to make plugin crash before entering engine_->HandleDocumentLoad, if called for deleted "Instance".
> Suspecting method call for deleted instance.
> 
> Example to explain why reset() makes difference:
> 
> scoped_ptr<int>* pt = NULL;
> {
>   scoped_ptr<int> t(new int);
>   pt = &t;
> }
> DCHECK(!(*pt));  // Fail
> {
>   scoped_ptr<int> t(new int);
>   pt = &t;
>   t.reset();
> }
> DCHECK(!(*pt)); // OK
> 
> BUG=372095, 372548
> 
> Review URL: https://codereview.chromium.org/300403002

TBR=vitalybuka@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=274854

[Vitaly Buka (NO REVIEWS), 2014-06-04 17:26:55]

Committed patchset #1 manually as r274854.