Add atom for per-process system ion heap size

The pulling code will be added in the next commit.

Bug: 130526489
Test: statsd_testdrive
Change-Id: I0fea4b6a7a8dbbdc574fb342c1e07aa0165bf797
(cherry picked from commit 77987ed47f5a0c11052c9f33f1d7933ca60e50b5)
3 files changed