Add event statistics to GCTracer.

src/gc-tracer.h

Index: src/gc-tracer.h
diff --git a/src/gc-tracer.h b/src/gc-tracer.h
index a9e02b3118daabca29bc07174d17d43c2ae223db..b1e5c5d0c6c243ecd3d2b26f4a00543ec0bb4bea 100644
--- a/src/gc-tracer.h
+++ b/src/gc-tracer.h
@@ -202,6 +202,36 @@ class GCTracer BASE_EMBEDDED {
   // Log an incremental marking step.
   void AddIncrementalMarkingStep(double duration);
 
+  // Compute the mean duration of the last scavenger events. Returns 0 if no
+  // events have been recorded.
+  double MeanScavengerDuration() const {
+    return MeanDuration(scavenger_events_);
+  }
+
+  // Compute the max duration of the last scavenger events. Returns 0 if no
+  // events have been recorded.
+  double MaxScavengerDuration() const { return MaxDuration(scavenger_events_); }
+
+  // Compute the mean duration of the last mark compactor events. Returns 0 if
+  // no events have been recorded.
+  double MeanMarkCompactorDuration() const {
+    return MeanDuration(mark_compactor_events_);
+  }
+
+  // Compute the max duration of the last mark compactor events. Return 0 if no
+  // events have been recorded.
+  double MaxMarkCompactorDuration() const {
+    return MaxDuration(mark_compactor_events_);
+  }
+
+  // Compute the mean step duration of the last incremental marking round.
+  // Returns 0 if no incremental marking round has been completed.
+  double MeanIncrementalMarkingDuration() const;
+
+  // Compute the max step duration of the last incremental marking round.
+  // Returns 0 if no incremental marking round has been completed.
+  double MaxIncrementalMarkingDuration() const;
+
  private:
   // Print one detailed trace line in name=value format.
   // TODO(ernstm): Move to Heap.
@@ -211,6 +241,12 @@ class GCTracer BASE_EMBEDDED {
   // TODO(ernstm): Move to Heap.
   void Print() const;
 
+  // Compute the mean duration of the events in the given ring buffer.
+  double MeanDuration(const EventBuffer& events) const;
+
+  // Compute the max duration of the events in the given ring buffer.
+  double MaxDuration(const EventBuffer& events) const;
+
   // Pointer to the heap that owns this tracer.
   Heap* heap_;