Add some comments.

Also, minor tweak to SurfaceTextureLayer.

Change-Id: If616d5ee4e8226dd0e16c5dbb0e0f80db553110e
diff --git a/services/surfaceflinger/SurfaceTextureLayer.h b/services/surfaceflinger/SurfaceTextureLayer.h
index 8baa8d2..a75ccf4 100644
--- a/services/surfaceflinger/SurfaceTextureLayer.h
+++ b/services/surfaceflinger/SurfaceTextureLayer.h
@@ -29,12 +29,17 @@
 
 class Layer;
 
+/*
+ * This is a thin wrapper around BufferQueue, used by the Layer class.
+ */
 class SurfaceTextureLayer : public BufferQueue
 {
 public:
     SurfaceTextureLayer();
     ~SurfaceTextureLayer();
 
+    // After calling the superclass connect(), set or clear synchronous
+    // mode appropriately for the specified API.
     virtual status_t connect(int api, QueueBufferOutput* output);
 };