graphics: count DCC/CMASK metadata readbacks in the performance overlay

src/graphics/presentation/performanceOverlay.cpp

@@ -310,6 +310,9 @@ void GpuActivityRows(const Snapshot& shown) {
 	Row("CPU waiting on GPU",
 	    Fmt("%.0f ms/s  (%.0f waits/s)", Rate(shown, Counter::GpuWaitNs) / 1e6,
 	        Rate(shown, Counter::GpuWaits)));
+	Row("DCC/CMASK readbacks",
+	    Fmt("%.0f ms/s  (%.0f/s)", Rate(shown, Counter::ColorMetadataReadbackNs) / 1e6,
+	        Rate(shown, Counter::ColorMetadataReadbacks)));
 }
 
 void CompilationRows(const Snapshot& shown) {