Fix spurious ANRs in native activities.

Some native activities experienced ANRs when the input consumer
deferred an input event due to client-side batching.  If the
input channel was fully emptied then the client had no way of
knowing that it should wake up to handle the deferred input event.

This patch also fixes some lock issues in the native activity
input queue implementation.  In at least one error case, it
was possible for a function to exit without releasing the lock.

Bug: 6051176
Change-Id: I4d9d843237e69b9834f8d8b360031b677fcab8c3