Syncs were being dropped when appIdleMode was on for an app. This CL backs off the sync instead of dropping it. When the app becomes non-idle, backoff is cleared and the sync is performed. Bug: 26355386 Change-Id: I2040dfd847011d3ca902e66a8cd52b2a429177c1 (cherry picked from commit 2c051498b2b0e2608740d906e70867b74083107d)