Replaces "nvpr mode" with "offscreen mode" and a flag to enable/
disable nvpr. Assigns new config names to the various combinations of
flags and begins printing them with the bench results in order to match
nanobench.
BUG=skia:
Review URL: https://codereview.chromium.org/1473253002
Modifies NvprWrappedBenchmark to present its offscreen canvas via
GrContext::copySurface rather than going through the SkCanvas API.
Only copies a subrectangle the size of the benchmark, not the entire
canvas.
BUG=skia:
Review URL: https://codereview.chromium.org/1443263002
