[heap] Add specific timer events for finalizing incremental GCs.

BUG=

Review URL: https://codereview.chromium.org/1375963003

Cr-Commit-Position: refs/heads/master@{#31103}

src/counters.h

@@ -488,6 +488,9 @@ double AggregatedMemoryHistogram<Histogram>::Aggregate(double current_ms,
 #define HISTOGRAM_TIMER_LIST(HT)                                              \
   /* Garbage collection timers. */                                            \
   HT(gc_compactor, V8.GCCompactor, 10000, MILLISECOND)                        \
+  HT(gc_finalize, V8.GCFinalzeMC, 10000, MILLISECOND)                         \
+  HT(gc_finalize_reduce_memory, V8.GCFinalizeMCReduceMemory, 10000,           \
+     MILLISECOND)                                                             \
   HT(gc_scavenger, V8.GCScavenger, 10000, MILLISECOND)                        \
   HT(gc_context, V8.GCContext, 10000,                                         \
      MILLISECOND) /* GC context cleanup time */                               \

src/heap/heap.cc

@@ -819,6 +819,23 @@ void Heap::OverApproximateWeakClosure(const char* gc_reason) {
 }
 
 
+HistogramTimer* Heap::GCTypeTimer(GarbageCollector collector) {
+  if (collector == SCAVENGER) {
+    return isolate_->counters()->gc_scavenger();
+  } else {
+    if (!incremental_marking()->IsStopped()) {
+      if (ShouldReduceMemory()) {
+        return isolate_->counters()->gc_finalize_reduce_memory();
+      } else {
+        return isolate_->counters()->gc_finalize();
+      }
+    } else {
+      return isolate_->counters()->gc_compactor();
+    }
+  }
+}
+
+
 void Heap::CollectAllGarbage(int flags, const char* gc_reason,
                              const v8::GCCallbackFlags gc_callback_flags) {
   // Since we are ignoring the return value, the exact choice of space does
@@ -964,9 +981,8 @@ bool Heap::CollectGarbage(GarbageCollector collector, const char* gc_reason,
     GarbageCollectionPrologue();
 
     {
-      HistogramTimerScope histogram_timer_scope(
-          (collector == SCAVENGER) ? isolate_->counters()->gc_scavenger()
-                                   : isolate_->counters()->gc_compactor());
+      HistogramTimerScope histogram_timer_scope(GCTypeTimer(collector));
+
       next_gc_likely_to_collect_more =
           PerformGarbageCollection(collector, gc_callback_flags);
     }

src/heap/heap.h

@@ -430,6 +430,7 @@ class GCIdleTimeHeapState;
 class GCTracer;
 class HeapObjectsFilter;
 class HeapStats;
+class HistogramTimer;
 class Isolate;
 class MemoryReducer;
 class ObjectStats;
@@ -1807,6 +1808,14 @@ class Heap {
   // objects that die later.
   void OverApproximateWeakClosure(const char* gc_reason);
 
+  // Returns the timer used for a given GC type.
+  // - GCScavenger: young generation GC
+  // - GCCompactor: full GC
+  // - GCFinalzeMC: finalization of incremental full GC
+  // - GCFinalizeMCReduceMemory: finalization of incremental full GC with
+  // memory reduction
+  HistogramTimer* GCTypeTimer(GarbageCollector collector);
+
   // ===========================================================================
   // Actual GC. ================================================================
   // ===========================================================================