BufferQueueProducer: add detachNextBuffer

Adds a new method, IGBP::detachNextBuffer, that effectively does
dequeue + request + detach in a single call, but does not need to
know anything about the dequeued buffer, and will not block on
dequeue. This is mostly for the upcoming StreamSplitter to use in
its onBufferReleased callback.

Change-Id: Ie88a69de109003acebaa486a5b44c8a455726550
diff --git a/include/gui/BufferQueue.h b/include/gui/BufferQueue.h
index da876ec..311926d 100644
--- a/include/gui/BufferQueue.h
+++ b/include/gui/BufferQueue.h
@@ -199,6 +199,10 @@
     // See IGraphicBufferProducer::detachBuffer
     virtual status_t detachProducerBuffer(int slot);
 
+    // See IGraphicBufferProducer::detachNextBuffer
+    virtual status_t detachNextBuffer(sp<GraphicBuffer>* outBuffer,
+            sp<Fence>* outFence);
+
     // See IGraphicBufferProducer::attachBuffer
     virtual status_t attachProducerBuffer(int* slot,
             const sp<GraphicBuffer>& buffer);