Add ::Leaky to the LazyInstance<SafeBrowsingServiceFactoryImpl> in
safe_browsing_service.cc.  Hopefully this will fix the "pure virtual method
called" errors seen in various ExtensionService tests that use safe browsing;
both those reverted as part of bug 233290, and the ones that are still live.

BUG=233290
R=jyasskin@chromium.org
TBR=shess@chromium.org

Review URL: https://codereview.chromium.org/60833007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@233426 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 233426