Print max RSS in GM and nanobench too.

Everyone used MB, so update the API to just return that.

BUG=skia:
R=halcanary@google.com, mtklein@google.com

Author: mtklein@chromium.org

Review URL: https://codereview.chromium.org/483323002
diff --git a/gyp/bench.gyp b/gyp/bench.gyp
index 398700f..d53e0f7 100644
--- a/gyp/bench.gyp
+++ b/gyp/bench.gyp
@@ -24,6 +24,7 @@
         'jsoncpp.gyp:jsoncpp',
         'skia_lib.gyp:skia_lib',
         'tools.gyp:crash_handler',
+        'tools.gyp:proc_stats',
         'tools.gyp:timer',
       ],
     },