Make scoped_ptr_malloc abort() on an invalid assignment.

(In particular, |foo = bar.Pass();| with foo.get() == bar.get().)

scoped_ptr already aborts on this.

R=brettw

Review URL: https://codereview.chromium.org/171533012

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@253407 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 253407