Adjust traces to diagnostic of HWC2on1Adapter

Change-Id: I0110fac372791bec657521522de3e08907f465f7
diff --git a/services/surfaceflinger/SurfaceFlinger.cpp b/services/surfaceflinger/SurfaceFlinger.cpp
index 2781e8c..e1dff3c 100644
--- a/services/surfaceflinger/SurfaceFlinger.cpp
+++ b/services/surfaceflinger/SurfaceFlinger.cpp
@@ -1265,6 +1265,7 @@
                             Fence::SIGNAL_TIME_PENDING);
             ATRACE_INT("FrameMissed", static_cast<int>(frameMissed));
             if (mPropagateBackpressure && frameMissed) {
+                ALOGD("Backpressure trigger, skipping transaction & refresh!");
                 signalLayerUpdate();
                 break;
             }