Replace WebScopedPtr with base's scoped_ptr in test runner library

BUG=331296
R=battre@chromium.org
TEST=none

Review URL: https://codereview.chromium.org/113943006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@242771 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 242771