Fix graphical glitches on Windows Mixed Reality

The issue here appears to be caused by a DiscardView() call, which tells
the GPU that we are done with a render target.  The contract is that
consumers of D3D11 are supposed to write to every pixel after discard,
which we may not be always doing, depending on viewport and scale.

Removing the DiscardView call fixes the graphics corruption. It may have
a small performance penalty, but that will be addressed in issue 938146.

Bug: 952371
Change-Id: I899d146aa1b93348114aad9e03abe2a9833fd6d6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1568774
Commit-Queue: Bill Orr <billorr@chromium.org>
Reviewed-by: Klaus Weidner <klausw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#651465}
1 file changed