camera2: skip capture result after clearZslQueue

After ZSL queue is cleared, don't add capture result to ZSL queue
if its corresponding buffer has been cleared.

Bug: 17185356
Change-Id: Iddac39ab09b2560e2ce9390895927217c1736d5a
diff --git a/services/camera/libcameraservice/gui/RingBufferConsumer.h b/services/camera/libcameraservice/gui/RingBufferConsumer.h
index a03736d..da97a11 100644
--- a/services/camera/libcameraservice/gui/RingBufferConsumer.h
+++ b/services/camera/libcameraservice/gui/RingBufferConsumer.h
@@ -159,6 +159,9 @@
     // Release all the non-pinned buffers in the ring buffer
     status_t clear();
 
+    // Return 0 if RingBuffer is empty, otherwise return timestamp of latest buffer.
+    nsecs_t getLatestTimestamp();
+
   private:
 
     // Override ConsumerBase::onFrameAvailable
@@ -180,6 +183,9 @@
     // List of acquired buffers in our ring buffer
     List<RingBufferItem>       mBufferItemList;
     const int                  mBufferCount;
+
+    // Timestamp of latest buffer
+    nsecs_t mLatestTimestamp;
 };
 
 } // namespace android