Make ScopedGenericObj compile with strict warnings when used with non-pointers.

No intended functionality change.  Required for a future clang roll.

BUG=none
TEST=none


Review URL: https://chromiumcodereview.appspot.com/10310183

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@137361 0039d316-1c4b-4281-b951-d872f2087c98