Direct3D: fix up tests

* Enable MipmappedTest
* Add didWriteToSurface calls to fix up MipmapInvalidation test
* Add flush & submit to fix DDLSkSurfaceFlush test

Change-Id: I9c3cad96b40491a54cab4edb8f56639d6cc16665
Bug: skia:10446
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/405496
Commit-Queue: Jim Van Verth <jvanverth@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
6 files changed