D3D11: Don't copy SharedSRVs around. This was causing a very large performance regression in Texture re-binding. Instead pass by const &, which should be fine, since values in std::map (and unordered_map) are not reallocated when the map changes. Also make the SharedResource type non-copyable, and add an explicit makeCopy method for when we need to clone the shared pointer. BUG=angleproject:2034 BUG=chromium:727318 Change-Id: I39508a6ca4b41e4da31fe68899caa4464138cada Reviewed-on: https://chromium-review.googlesource.com/517670 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Corentin Wallez <cwallez@chromium.org>