Update bench to be able to preprocess skps

tools/bench_pictures_main.cpp

Index: tools/bench_pictures_main.cpp
===================================================================
--- tools/bench_pictures_main.cpp	(revision 14136)
+++ tools/bench_pictures_main.cpp	(working copy)
@@ -49,6 +49,8 @@
             "SK_LAZY_CACHE_STATS set to true. Report percentage of cache hits when using "
             "deferred image decoding.");
 
+DEFINE_bool(preprocess, false, "If true, perform device specific preprocessing before timing.");
+
 static char const * const gFilterTypes[] = {
     "paint",
     "point",
@@ -341,6 +343,7 @@
     }
 
     benchmark->setPurgeDecodedTex(FLAGS_purgeDecodedTex);
+    benchmark->setPreprocess(FLAGS_preprocess);
 
     if (FLAGS_readPath.count() < 1) {
         gLogger.logError(".skp files or directories are required.\n");