This allows us to report the "native heap memory" value in
the Observatory for VMs running on Fuchsia.
This change also renames the flag --enable-malloc-hooks to
--profiler-native-memory to better reflect what the flag
does. (In the future we may also want to rename
--profiler to --profiler-cpu.)
R=rmacnak@google.com
Review-Url: https://codereview.chromium.org/2829833003 .