Add sideband streams to BufferQueue and related classes

Sideband streams are essentially a device-specific buffer queue that
bypasses the BufferQueue system. They can be used for situations with
hard real-time requirements like high-quality TV and video playback
with A/V sync. A handle to the stream is provided by the source HAL,
and attached to a BufferQueue. The sink HAL can read buffers via the
stream handle rather than acquiring individual buffers from the
BufferQueue.

Change-Id: Ib3f262eddfc520f4bbe3d9b91753ed7dd09d3a9b
diff --git a/include/gui/BufferQueueConsumer.h b/include/gui/BufferQueueConsumer.h
index 20db98c..2bdcf28 100644
--- a/include/gui/BufferQueueConsumer.h
+++ b/include/gui/BufferQueueConsumer.h
@@ -133,6 +133,9 @@
     // NATIVE_WINDOW_TRANSFORM_ROT_90.  The default is 0 (no transform).
     virtual status_t setTransformHint(uint32_t hint);
 
+    // Retrieve the sideband buffer stream, if any.
+    virtual sp<NativeHandle> getSidebandStream() const;
+
     // dump our state in a String
     virtual void dump(String8& result, const char* prefix) const;