Changes

tmf.ui: Accelerate tree drawing for TimeGraphControl

Bug: 576066

The tree re-calculates its font size for every row. Cache it per-frame.

Lowers draw time

          before  after
Min       218 us  110 us
Max       215 ms  110 ms
Avg        45 ms   30 ms
Stdev      30 ms   16 ms

This does not fix the problem, but significantly reduces it.

[Changed] Improved performance of trees in TimeGraphControl

Change-Id: Iff9e3bdfdce2c69713c01f151f4aa1c5aabb8e95
Signed-off-by: Matthew Khouzam <matthew.khouzam@ericsson.com>