The resource manager tracks the allocations and deallocations of all
D3D11 resources that have device memory: Buffers and Textures (which
are either 2D or 3D). It also tracks the number of active Views (DSV,
RTV, and SRV, potentially UAV with ES 3.1).

A new smart pointer type will wrap the resource deallocation so that
the object notifies the manager when ANGLE is done with the resouce.
This allows us to track precisely how much GPU memory we think we're
using at any point, and will help prevent resource leaks for these
object types. It also makes initialization and releasing much more
trivial.

The base class for a resource uses a template template parameter so
that we can use a unique or shared pointer depending on if the object
in question needs unique or shared ownership. For some resources
(in our case, SRVs are shared between the TextureStorage11 and
RenderTarget11 classes, and Textures are shared in many places) we
need to have the ability to have shared ownership. Unique ownership is
a little bit more efficient so supporting both can be helpful.

In this patch RenderTargetView allocation is moved to use the unique
smart pointer.

BUG=angleproject:2034

Change-Id: Idb1245c24cd66733b8b5ca524c727350b2d2c745
Reviewed-on: https://chromium-review.googlesource.com/503248
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>