Fix some const-ness and comments

mDrawingState doesn't need to be accessed by the
mStateLock, because by definition it's only accessed
from the main thread.

Similarily, the list of layers in the drawing state
cannot change (ie: is const).

Change-Id: I2e5da7f4d8caee7af7802b432cd45cc81c7c08b0
2 files changed