SurfaceFlinger: add Refresh Rate overlay

Add an overlay to indicate what is the current refresh rate.
Currently it is implemented by a ColorLayer:
 - Red - Default refresh rate
 - Green - Performance refresh rate

To enable the overlay:
adb shell service call SurfaceFlinger 1034 i32 1
To disable the overlay:
adb shell service call SurfaceFlinger 1034 i32 0

Test: manual
Change-Id: I851f2530e7accacd2cac446b30aa2e0b6d431a92