BQ: Allow shared buffer to be the first queued buffer

- When single-buffer mode is enabled the shared buffer will now be
  either the first buffer dequeued or the first buffer queued.
  Whichever comes first.

Bug 24940410

Change-Id: I9f7e2630640e37fe1fb967aed41a3025567247a8
diff --git a/include/gui/IGraphicBufferProducer.h b/include/gui/IGraphicBufferProducer.h
index f6b4230..fee7c63 100644
--- a/include/gui/IGraphicBufferProducer.h
+++ b/include/gui/IGraphicBufferProducer.h
@@ -526,9 +526,10 @@
 
     // Used to enable/disable single buffer mode.
     //
-    // In single buffer mode the last buffer that was dequeued will be cached
-    // and returned to all calls to dequeueBuffer and acquireBuffer. This allows
-    // the producer and consumer to simultaneously access the same buffer.
+    // When single buffer mode is enabled the first buffer that is queued or
+    // dequeued will be cached and returned to all subsequent calls to
+    // dequeueBuffer and acquireBuffer. This allows the producer and consumer to
+    // simultaneously access the same buffer.
     virtual status_t setSingleBufferMode(bool singleBufferMode) = 0;
 
     // Used to enable/disable auto-refresh.