BQ: Improved buffer/slot tracking

- Explicitly track active buffers and unused slots on top of the
  already existing tracking for free slots and free buffers.

Change-Id: Ife2678678e96f0eb0b3fb21571058378134bd868
diff --git a/include/gui/IGraphicBufferConsumer.h b/include/gui/IGraphicBufferConsumer.h
index d4c9ee5..ebce7fb 100644
--- a/include/gui/IGraphicBufferConsumer.h
+++ b/include/gui/IGraphicBufferConsumer.h
@@ -199,7 +199,9 @@
     // cannot be less than maxAcquiredBufferCount.
     //
     // Return of a value other than NO_ERROR means an error has occurred:
-    // * BAD_VALUE - bufferCount was out of range (see above).
+    // * BAD_VALUE - one of the below conditions occurred:
+    //             * bufferCount was out of range (see above).
+    //             * failure to adjust the number of available slots.
     // * INVALID_OPERATION - attempting to call this after a producer connected.
     virtual status_t setMaxBufferCount(int bufferCount) = 0;
 
@@ -212,7 +214,9 @@
     // to be exceeded.
     //
     // Return of a value other than NO_ERROR means an error has occurred:
-    // * BAD_VALUE - maxAcquiredBuffers was out of range (see above).
+    // * BAD_VALUE - one of the below conditions occurred:
+    //             * maxAcquiredBuffers was out of range (see above).
+    //             * failure to adjust the number of available slots.
     // * INVALID_OPERATION - attempting to call this after a producer connected.
     virtual status_t setMaxAcquiredBufferCount(int maxAcquiredBuffers) = 0;