Switch the WebstoreDataFetcherDelegate::OnWebstoreResponseParseSuccess interface to scoped_ptr.

Re-land of r232877 which was missing an include.

Fixes memory leaks.

BUG=313695
R=benwells@chromium.org, satorux@chromium.org
TBR=benwells@chromium.org, satorux@chromium.org

Review URL: https://codereview.chromium.org/59663002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@233253 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 233253