Bug 1145295 - Add some debug logging to try and trace an intermittent assertion. r=nical

gfx/layers/ipc/CompositorParent.cpp

@@ -1121,6 +1121,14 @@ CompositorParent::ShadowLayersUpdated(LayerTransactionParent* aLayerTree,
         mRootLayerTreeID, aPaintSequenceNumber);
   }
 
+#ifdef DEBUG
+  if (aTransactionId <= mPendingTransaction) {
+    // Logging added to help diagnose why we're triggering the assert below.
+    // See bug 1145295
+    printf_stderr("CRASH: aTransactionId %" PRIu64 " <= mPendingTransaction %" PRIu64 "\n",
+      aTransactionId, mPendingTransaction);
+  }
+#endif
   MOZ_ASSERT(aTransactionId > mPendingTransaction);
   mPendingTransaction = aTransactionId;