D3D11: If an image is dirty, copy it to the storage before copying from a FB. If a storage already existed, it may have old data in it. Check if the image is dirty and copy the initialized memory into the storage before copying data from the framebuffer. TEST=conformance/textures/misc/copy-tex-image-and-sub-image-2d BUG=angleproject:1815 Change-Id: Ic69c5519b2e09e4b62025b1bf413d2a71a4a2afb Reviewed-on: https://chromium-review.googlesource.com/568410 Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Geoff Lang <geofflang@chromium.org>