[heap] Add histogram counter for incremental marking time per GC cycle.

The name of the histogram is V8.GCIncrementalMarkingSum.

Bug: chromium:756592
Change-Id: Ib073e846054550cce8558a3a577a0451e3182407
Reviewed-on: https://chromium-review.googlesource.com/618877
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47422}

src/counters.h

@@ -991,12 +991,13 @@ class RuntimeCallTimerScope {
 };
 
 #define HISTOGRAM_RANGE_LIST(HR)                                              \
-  /* Generic range histograms */                                              \
+  /* Generic range histograms: HR(name, caption, min, max, num_buckets) */    \
   HR(detached_context_age_in_gc, V8.DetachedContextAgeInGC, 0, 20, 21)        \
   HR(code_cache_reject_reason, V8.CodeCacheRejectReason, 1, 6, 6)             \
   HR(errors_thrown_per_context, V8.ErrorsThrownPerContext, 0, 200, 20)        \
   HR(debug_feature_usage, V8.DebugFeatureUsage, 1, 7, 7)                      \
   HR(incremental_marking_reason, V8.GCIncrementalMarkingReason, 0, 21, 22)    \
+  HR(incremental_marking_sum, V8.GCIncrementalMarkingSum, 0, 10000, 101)      \
   HR(mark_compact_reason, V8.GCMarkCompactReason, 0, 21, 22)                  \
   HR(scavenge_reason, V8.GCScavengeReason, 0, 21, 22)                         \
   HR(young_generation_handling, V8.GCYoungGenerationHandling, 0, 2, 3)        \

src/heap/gc-tracer.cc

@@ -217,6 +217,10 @@ void GCTracer::Start(GarbageCollector collector,
 }
 
 void GCTracer::ResetIncrementalMarkingCounters() {
+  if (incremental_marking_duration_ > 0) {
+    heap_->isolate()->counters()->incremental_marking_sum()->AddSample(
+        static_cast<int>(incremental_marking_duration_));
+  }
   incremental_marking_bytes_ = 0;
   incremental_marking_duration_ = 0;
   for (int i = 0; i < Scope::NUMBER_OF_INCREMENTAL_SCOPES; i++) {