qssi: Disable Skia tracing by default

If the prop "debug.hwui.skia_atrace_enabled" is enabled, too many
skia tracing calls will be printed in every frame. This has obvious
overhead on performance/power, and can cause many janks. So disable
it by default, and user can set it manually if necessary.

Change-Id: I5d470b22a643634bdd7db9f307c29deae6ff176f
1 file changed