Samples: clean up cruft

  - replace virtual with override.
  - remove default constructor.
  - use default field initializers
  - move work from constructor into onOnceBeforeDraw
  - mark everything private
  - enum { N = 100 }; constants to constexpr
  - remove unused variables

Change-Id: I8c7a19bc24fec416a6b88d634ee948d3e842b986
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/228056
Commit-Queue: Ben Wagner <bungeman@google.com>
Auto-Submit: Hal Canary <halcanary@google.com>
Reviewed-by: Ben Wagner <bungeman@google.com>
19 files changed