ui freeze workaround: reenable triple buffering mode

we're seeing UI freezes when window updates and
composition are separated. for now we workaround this
by always doing a composition after window updates on
vsync. triple buffering is reenabled for performance.

Change-Id: I693d705000b7452489bb0b4918fbeadb9879315c
diff --git a/services/surfaceflinger/Layer.cpp b/services/surfaceflinger/Layer.cpp
index 64f72d5..3e6b872 100644
--- a/services/surfaceflinger/Layer.cpp
+++ b/services/surfaceflinger/Layer.cpp
@@ -98,7 +98,12 @@
     mSurfaceTexture = new SurfaceTextureLayer(mTextureName, this);
     mSurfaceTexture->setFrameAvailableListener(new FrameQueuedListener(this));
     mSurfaceTexture->setSynchronousMode(true);
+#ifdef USE_TRIPLE_BUFFERING
+#warning "using triple buffering"
+    mSurfaceTexture->setBufferCountServer(3);
+#else
     mSurfaceTexture->setBufferCountServer(2);
+#endif
 }
 
 Layer::~Layer()