The transaction flags were atomically read-and-cleared to determine if
a transaction was needed, in the later case, mStateLock was taken to
keep the current state still during the transaction. This left a small
window open, where a layer could be removed after the transaction flags
were checked but before the transaction was started holding the lock.
In that situation eTraversalNeeded would be set but only seen during the
next transaction cycle; however, because we're handling this transaction
(because of another flag) it will be commited, "loosing" the information
about the layer being removed -- so when the next transaction cycle due
to eTraversalNeeded starts, it won't notice that layers have been removed
and won't populated the ditchedLayers array.
Bug: 4483049
Change-Id: Ibb5989312f871339928ee1aa3f9567770d72969b
34cd9b72f1