libgui: Add getLastQueuedBuffer to BufferQueue

Adds the ability to get the last buffer queued to a BufferQueue plus
its acquire fence.

Bug: 27708453
Change-Id: Iee39475740b40c854a5f46178b2934fd930e61b8
diff --git a/include/gui/Surface.h b/include/gui/Surface.h
index f76a9be..bbf427d 100644
--- a/include/gui/Surface.h
+++ b/include/gui/Surface.h
@@ -129,6 +129,10 @@
      */
     bool waitForNextFrame(uint64_t lastFrame, nsecs_t timeout);
 
+    // See IGraphicBufferProducer::getLastQueuedBuffer
+    status_t getLastQueuedBuffer(sp<GraphicBuffer>* outBuffer,
+            sp<Fence>* outFence);
+
 protected:
     virtual ~Surface();