More scaffolding, add class ServiceWorkerProviderHost.

BUG=285976

Review URL: https://codereview.chromium.org/70533005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@236872 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 236872
Add missing histogram definition for signin confirmations.

BUG=

Review URL: https://codereview.chromium.org/82733007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@236873 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 236873