Merge latest green inbound changeset and mozilla-central
Bug 878493 - DeviceStorage: Invalidate used space cache if free space changes. r=janv
Bug 876936 - Alarms set to a past time fire immediately instead of error. r=gene
Bug 879214 - Try to fix race condition in test_audio_wakelock.html. r=baku

--HG--
extra : rebase_source : af1d40db2ed8395db183a14a229ad49e4bc36bf8
Merge birch to m-c.
Merge inbound to m-c.
Merge m-c to inbound.