fix a small bug that caused screenshot to show garbage in some cases
fix a small bug that caused screenshot to show garbage in some cases

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

Change-Id: Ie9ab9b94eabfa6cafddf45bb14bc733bdc8d35c0

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