Added histogram to track distribution of requested idle notifications.

src/counters.h

Index: src/counters.h
diff --git a/src/counters.h b/src/counters.h
index 4a35bf493f2c24809d742e31fcdc2c8db406f360..38fe43c3a6733e6096ab4bf98633d92a432e6d41 100644
--- a/src/counters.h
+++ b/src/counters.h
@@ -291,6 +291,8 @@ class HistogramTimerScope BASE_EMBEDDED {
 #endif
 };
 
+#define HISTOGRAM_RANGE_LIST(HR) \
+  HR(gc_idle_time_allotted_in_ms, V8.GCIdleTimeAllottedInMS)
 
 #define HISTOGRAM_TIMER_LIST(HT)                             \
   /* Garbage collection timers. */                           \
@@ -551,6 +553,11 @@ class HistogramTimerScope BASE_EMBEDDED {
 // This file contains all the v8 counters that are in use.
 class Counters {
  public:
+#define HR(name, caption) \
+  Histogram* name() { return &name##_; }
+  HISTOGRAM_RANGE_LIST(HR)
+#undef HR
+
 #define HT(name, caption) \
   HistogramTimer* name() { return &name##_; }
   HISTOGRAM_TIMER_LIST(HT)
@@ -638,6 +645,10 @@ class Counters {
   void ResetHistograms();
 
  private:
+#define HR(name, caption) Histogram name##_;
+  HISTOGRAM_RANGE_LIST(HR)
+#undef HR
+
 #define HT(name, caption) \
   HistogramTimer name##_;
   HISTOGRAM_TIMER_LIST(HT)