Make applying gamma less laggy.

Applying gamma takes a while, so optimize out multiple set requests
occuring quickly after each other. Those appear e.g. when dragging the
sliders quickly.

Change-Id: I48c71b8e041679bcce932f99d198f4e6a027010a
Merge remote-tracking branch 'upstream/cm-10.2' into dark-jelly-cm-10.2