[libui/sf] Add total buffer size tracing to SF

Adds a line for "Total Buffer Size" to systrace, corresponding to the
combined size of all buffers allocated in SF's process.

Test: manual, verified that line appears on systrace and matches dumpsys
Bug: 131244853
Change-Id: Ifdd3151516dd5010494c9619281a0f0b71767e9c
3 files changed