Remove warnings, improve benchmark quality, complicate benchmark results:  - data on heap instead of stack  - more closely match operations of actual SkMatrix::setConcat()  - avoid random perturbations, do_always;    use perf annotate to verify that assembly isn't getting optimized away
Remove warnings, improve benchmark quality, complicate benchmark results:
 - data on heap instead of stack
 - more closely match operations of actual SkMatrix::setConcat()
 - avoid random perturbations, do_always;
   use perf annotate to verify that assembly isn't getting optimized away



csulmone/skia,csulmone/skia,csulmone/skia,csulmone/skia