SKPs-as-benches in nanobench

This is meant to replace bench_pictures.

CQ_EXTRA_TRYBOTS=tryserver.skia:Build-Mac10.7-Clang-Arm7-Release-iOS-Trybot

BUG=skia:
R=bsalomon@google.com, jcgregorio@google.com, mtklein@google.com

Author: mtklein@chromium.org

Review URL: https://codereview.chromium.org/425393004
diff --git a/tools/flags/SkCommonFlags.h b/tools/flags/SkCommonFlags.h
index a30d1ae..4abf201 100644
--- a/tools/flags/SkCommonFlags.h
+++ b/tools/flags/SkCommonFlags.h
@@ -21,6 +21,7 @@
 DECLARE_bool(resetGpuContext);
 DECLARE_bool(abandonGpuContext);
 DECLARE_bool(single);
+DECLARE_string(skps);
 DECLARE_int32(threads);
 DECLARE_string(resourcePath);
 DECLARE_bool(verbose);