This change also moves all SRV storage to use the custom smart
pointer classes in ResourceManager11. Every single SRV is now
allocated in ResourceManager11. For TextureStorage11 and
RenderTarget11, we use a shared pointer type since the SRVs use
shared ownership by both classes.

BUG=angleproject:2034

Change-Id: I90666fbbbc23ff10870b7401f3da09ef79258136
Reviewed-on: https://chromium-review.googlesource.com/503250Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>