Move productSub/vendor/vendorSub to Navigator class

Move productSub/vendor/vendorSub getters from NavigatorBase to Navigator
as this is not shared with WorkerNavigator nor do we intent to since
this is an old non-standard API.

Also measure usage for this non-standard API to help us determine if
we can deprecate them.

R=arv@chromium.org, haraken@chromium.org

Review URL: https://codereview.chromium.org/22929011

git-svn-id: svn://svn.chromium.org/blink/trunk@156399 bbb929c8-8fbe-4397-9dbb-9b2b20218538