Bug 449523 - CircularBuffer setBufferSize to smaller should omit oldest
data instead of lateset

Fix the bug. Clean up code. Use system default font as default font.

Change-Id: Ib4b4798dff38dfc65b45255a1ef7b2a5b1a14ec5
Signed-off-by: Xihui Chen <ztyaner11@gmail.com>