[heap] Fix marking throughput computation

Exclude embedder tracing time

Bug: chromium:945806
Change-Id: I9719a42f86fd6edad8fd2b0f707b4dc7feada277
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1564437Reviewed-by: Hannes Payer <hpayer@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60783}

src/heap/gc-tracer.cc

@@ -1136,9 +1136,16 @@ void GCTracer::RecordGCPhasesHistograms(TimedHistogram* gc_timer) {
     if (base::TimeTicks::IsHighResolution() &&
         heap_->SizeOfObjects() > kMinObjectSizeForReportingThroughput) {
       DCHECK_GT(overall_marking_time, 0.0);
+      const double overall_v8_marking_time =
+          overall_marking_time -
+          current_.scopes[Scope::MC_MARK_EMBEDDER_PROLOGUE] -
+          current_.scopes[Scope::MC_MARK_EMBEDDER_TRACING] -
+          current_.scopes[Scope::MC_INCREMENTAL_EMBEDDER_PROLOGUE] -
+          current_.scopes[Scope::MC_INCREMENTAL_EMBEDDER_TRACING];
+      DCHECK_GT(overall_v8_marking_time, 0.0);
       const int main_thread_marking_throughput_mb_per_s =
           static_cast<int>(static_cast<double>(heap_->SizeOfObjects()) /
-                           overall_marking_time * 1000 / 1024 / 1024);
+                           overall_v8_marking_time * 1000 / 1024 / 1024);
       heap_->isolate()
           ->counters()
           ->gc_main_thread_marking_throughput()