Rename single buffer mode to shared buffer mode

Change-Id: Id43d0737d9367981644e498942ebc0077d61038c
(cherry picked from commit 3559fbf93801e2c0d9d8fb246fb9b867a361b464)
diff --git a/include/gui/BufferSlot.h b/include/gui/BufferSlot.h
index 943fa82..57704b1 100644
--- a/include/gui/BufferSlot.h
+++ b/include/gui/BufferSlot.h
@@ -79,7 +79,7 @@
     // transitions to FREE when releaseBuffer (or detachBuffer) is called. A
     // detached buffer can also enter the ACQUIRED state via attachBuffer.
     //
-    // SHARED indicates that this buffer is being used in single-buffer
+    // SHARED indicates that this buffer is being used in shared buffer
     // mode. It can be in any combination of the other states at the same time,
     // except for FREE (since that excludes being in any other state). It can
     // also be dequeued, queued, or acquired multiple times.