Support --dryRun in nanobench to get a list of benchmarks.

bench/nanobench.cpp

Index: bench/nanobench.cpp
diff --git a/bench/nanobench.cpp b/bench/nanobench.cpp
index 31efefa4f4fb0034a632143bed2107b18bbe221b..aeae4f41dbea383548f1d74e7590fa8875c3d2a1 100644
--- a/bench/nanobench.cpp
+++ b/bench/nanobench.cpp
@@ -1082,10 +1082,13 @@ int nanobench_main() {
             SkCanvas* canvas = target->getCanvas();
             const char* config = target->config.name.c_str();
 
-            if (FLAGS_pre_log) {
+            if (FLAGS_pre_log || FLAGS_dryRun) {
                 SkDebugf("Running %s\t%s\n"
                          , bench->getUniqueName()
                          , config);
+                if (FLAGS_dryRun) {
+                    continue;
+                }
             }
 
             target->setup();