Merge third_party/angle_dx11 from https://chromium.googlesource.com/external/angle.git at a9ca4ac5b94886b4b9d7e957c375e60ea9a68d8a

This commit was generated by merge_from_chromium.py.

Change-Id: I68bf13e461a4becbc8f03afc491024901967cff3