Created a subscriber function onLabelUpdated in the storage base
class. The derived storage class will pass the label reference to
the base storage class in the constructor. Future changes will use
this label reference to update the label string with D3D.

Bug: chromium:1164111
Change-Id: Ic5ca73bac61427afe392bb5bcc6a6eab8e785941
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2981451Reviewed-by: Rafael Cintron <rafael.cintron@microsoft.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Rafael Cintron <rafael.cintron@microsoft.com>