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
This change updates a small subset of benchmarks to flush the GrContext
between draw loops (specifically SKP benchmarks, SampleApp, and the
warmup in visualbench). This helps improve timing accuracy by not
allowing the gpu to batch across draw boundaries in the affected
benchmarks.
BUG=skia:
Review URL: https://codereview.chromium.org/1427533002
