Add equality/inequality tests to KeyTest.
Add equality/inequality tests to KeyTest.

Previously, we didn't seem to have any tests verifying the behavior of
operator== and operator!=.

Change-Id: I1f76b8307a551f687d172782e8a30a01c0718e85
Bug: skia:13428
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/549837
Auto-Submit: John Stiles <f4fcf42d3bb5924557f1eeb3be66747535e585da@google.com>
Reviewed-by: Robert Phillips <95e8ac5504948c7bf91b22c16a8dbb7ae7c66bfd@google.com>

google/skia,google/skia,google/skia,google/skia,google/skia,google/skia,google/skia,google/skia,google/skia,google/skia