Revert "Revert "SurfaceFlinger: add a sysprop for GL backpressure""

This reverts commit cc1ce6476e4deb8877c10b2a59afd27556ec72e9.

Reason for revert: This change is needed to fix b/138083790. The underlying issue causing the first revert is now resolved.

Change-Id: I82eeec5f5e66570e03f37294d7bbe15c41fec86e
2 files changed