Make the credential storage change action public.

Bug: 6009802

When the credential storage changes, (adding/removing certs,
resetting the storage, enabling/disabling trusted CAs, etc), the
applications that use the storage has to be made aware of the
fact that the storage changed, so they can clear any cached state,
close connections or take any other actions. Internally, this
applies to webview. However, applications, potentially including
3rd party browsers, also need this information.

Change-Id: I765b97a3f38f45247ee3f6e127b490388d373847