GitLab

The service is not a SchemaRegistry anymore but owns one instead. This
enables the service to own subclasses of SchemaRegistry.

Also added a ForwardingSchemaRegisy, which wraps another
SchemaRegistry. This will be used in a future CL.

R=bartfab@chromium.org
TBR=kalman@chromium.org
BUG=224596

Review URL: https://codereview.chromium.org/349643002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@278735 0039d316-1c4b-4281-b951-d872f2087c98