Fix GL MSAA support in Mac Viewer.

The Mac GLContext is designed to not constantly teardown on resizes
and minor DisplayParams changes. However, for MSAA we do have to
tear it down.

Change-Id: I1a9d765068fa5f6b22dff49f6355c29e1affb686
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/226850
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
2 files changed