Rename single buffer mode to shared buffer mode

Change-Id: Id43d0737d9367981644e498942ebc0077d61038c
(cherry picked from commit 3559fbf93801e2c0d9d8fb246fb9b867a361b464)
diff --git a/services/surfaceflinger/Layer.cpp b/services/surfaceflinger/Layer.cpp
index 65b11a5..2eedee4 100644
--- a/services/surfaceflinger/Layer.cpp
+++ b/services/surfaceflinger/Layer.cpp
@@ -1882,7 +1882,7 @@
 
         // This boolean is used to make sure that SurfaceFlinger's shadow copy
         // of the buffer queue isn't modified when the buffer queue is returning
-        // BufferItem's that weren't actually queued. This can happen in single
+        // BufferItem's that weren't actually queued. This can happen in shared
         // buffer mode.
         bool queuedBuffer = false;
         status_t updateResult = mSurfaceFlingerConsumer->updateTexImage(&r,