fix a small bug that caused screenshot to show garbage in some cases (DO NOT MERGE)
fix a small bug that caused screenshot to show garbage in some cases (DO NOT MERGE)

we were not clearing the screen entirely, which caused garbage when
the screen wasn't entirely covered by windows.

Change-Id: Ia7aa13c36a8a314e0e8427d419b16b9aa2165ddf

xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base