nanobench: upload peak memory usage as its own trace.

We'll end up with a result like this:
      "memory_usage" : {
         "meta" : {
            "max_rss_mb" : 57
         }
      }

BUG=skia:

Review URL: https://codereview.chromium.org/780013002

1 files changed, 4 insertions, 0 deletions

diff --git a/bench/nanobench.cpp b/bench/nanobench.cpp
index 3f8919d260..a64cbcaf1f 100644
--- a/bench/nanobench.cpp
+++ b/bench/nanobench.cpp
@@ -793,6 +793,10 @@ int nanobench_main() {
 #endif
     }
 
+    log->bench("memory_usage", 0,0);
+    log->config("meta");
+    log->metric("max_rss_mb", sk_tools::getMaxResidentSetSizeMB());
+
     return 0;
 }