Fix sockfd leakage in SensorService.

i) Call removeFd() only if the fd in the BitTube has been
previously added to the Looper. Use a flag to determine whether the fd
has been previously added or not.
ii) Increment mPendingFlushEventsToSend after holding a connectionLock.
iii) Store the number of acks that are pending in SensorEventQueue
 and send them all at once.

Bug: 17472228
Change-Id: I1ec834fea1112a9cfbd9cddd2198438793698502
diff --git a/include/gui/SensorEventQueue.h b/include/gui/SensorEventQueue.h
index 019308d..02b3d38 100644
--- a/include/gui/SensorEventQueue.h
+++ b/include/gui/SensorEventQueue.h
@@ -86,6 +86,7 @@
     ASensorEvent* mRecBuffer;
     size_t mAvailable;
     size_t mConsumed;
+    uint32_t mNumAcksToSend;
 };
 
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