Move threaded BMP device to samples

Currently only referenced by SampleApp, and this squelches false positive
warnings from Clang's thread safety analysis when clients build this code.

Bug: skia:
Change-Id: I710fdc882e05fc5b80977139237028d1408f17db
Reviewed-on: https://skia-review.googlesource.com/20831
Commit-Queue: Brian Osman <brianosman@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>
Reviewed-by: Mike Klein <mtklein@chromium.org>
2 files changed