Add aggregation method to dumputils

Will be used for aggregating process states together for stats tracking
and output.

Change-Id: I5833a53f2e5e788d0475e10129658d12d9cf2b88
Bug: 148542701
Merged-In: I5833a53f2e5e788d0475e10129658d12d9cf2b88
Test: build, flash, unit tests (newly added code is not invoked yet)
(cherry picked from commit b832e988)