to help debugging [2461567] Home screen redraw messed up

log SF's idea of the front buffer in dumpsys.
diff --git a/libs/surfaceflinger/Layer.h b/libs/surfaceflinger/Layer.h
index 1310ecc..743afb4 100644
--- a/libs/surfaceflinger/Layer.h
+++ b/libs/surfaceflinger/Layer.h
@@ -78,6 +78,8 @@
     inline const sp<FreezeLock>&  getFreezeLock() const { return mFreezeLock; }
     // only for debugging
     inline PixelFormat pixelFormat() const { return mFormat; }
+    // only for debugging
+    inline int getFrontBufferIndex() const { return mFrontBufferIndex; }
 
 private:
     inline sp<GraphicBuffer> getFrontBufferLocked() {
diff --git a/libs/surfaceflinger/SurfaceFlinger.cpp b/libs/surfaceflinger/SurfaceFlinger.cpp
index b408779..4555b3c 100644
--- a/libs/surfaceflinger/SurfaceFlinger.cpp
+++ b/libs/surfaceflinger/SurfaceFlinger.cpp
@@ -1519,6 +1519,10 @@
             if (l != 0) {
                 SharedBufferStack::Statistics stats = l->lcblk->getStats();
                 result.append( l->lcblk->dump("      ") );
+                snprintf(buffer, SIZE,
+                        "      front-index=%u\n", l->getFrontBufferIndex());
+                result.append(buffer);
+
                 sp<const GraphicBuffer> buf0(l->getBuffer(0));
                 sp<const GraphicBuffer> buf1(l->getBuffer(1));
                 uint32_t w0=0, h0=0, s0=0;