glCopyTextureCHROMIUM calls in D3D11 would call getNativeTexture on the
copy source which would allocate a TextureStorage11 if one did not
already exist. This caused full mip-chain allocations in some cases when
we could have just copied directly from the staging Image11.
When navigating to wikipedia.org:
Peak memory | Stable memory
Passthrough (before): 142 mb | 119 mb
Passthrough (after): 138 mb | 106 mb
Validating: 139 mb | 110 mb
No mip-mapped textures were allocated after this change.
BUG=chromium:1030835
Change-Id: Icd14afaec445299423cfea293cba501d774f6ade
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2028147
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Rafael Cintron <rafael.cintron@microsoft.com>
