Adding a metric to track only the checkerboarding.

cc/debug/rendering_stats_instrumentation.cc

Index: cc/debug/rendering_stats_instrumentation.cc
diff --git a/cc/debug/rendering_stats_instrumentation.cc b/cc/debug/rendering_stats_instrumentation.cc
index 4a28a66ac8d7fa6113bd073dcd39c63ebb16c781..7497c628ed19fa4abbee21bb5558967a79a3d68b 100644
--- a/cc/debug/rendering_stats_instrumentation.cc
+++ b/cc/debug/rendering_stats_instrumentation.cc
@@ -81,6 +81,15 @@ void RenderingStatsInstrumentation::AddApproximatedVisibleContentArea(
   impl_thread_rendering_stats_.approximated_visible_content_area += area;
 }
 
+void RenderingStatsInstrumentation::AddCheckerboardedVisibleContentArea(
+    int64 area) {
+  if (!record_rendering_stats_)
+    return;
+
+  base::AutoLock scoped_lock(lock_);
+  impl_thread_rendering_stats_.checkerboarded_visible_content_area += area;
+}
+
 void RenderingStatsInstrumentation::AddDrawDuration(
     base::TimeDelta draw_duration,
     base::TimeDelta draw_duration_estimate) {