[counters] adding more counters and log-events

src/counters.h

Index: src/counters.h
diff --git a/src/counters.h b/src/counters.h
index d8a3f091f848b3c46ab159ca2120ae34392243ab..71bfde84714f3153e32648e9c3e82ea9e84bd61a 100644
--- a/src/counters.h
+++ b/src/counters.h
@@ -328,8 +328,9 @@ class AggregatableHistogramTimer : public Histogram {
   base::TimeDelta time_;
 };
 
-
-// A helper class for use with AggregatableHistogramTimer.
+// A helper class for use with AggregatableHistogramTimer. This is the
+// outer-most timer scope used with an AggregatableHistogramTimer. It will
+// aggregate the information from the inner AggregatedHistogramTimerScope.
 class AggregatingHistogramTimerScope {
  public:
   explicit AggregatingHistogramTimerScope(AggregatableHistogramTimer* histogram)
@@ -342,8 +343,8 @@ class AggregatingHistogramTimerScope {
   AggregatableHistogramTimer* histogram_;
 };
 
-
-// A helper class for use with AggregatableHistogramTimer.
+// A helper class for use with AggregatableHistogramTimer, the "inner" scope
+// which defines the events to be timed.
 class AggregatedHistogramTimerScope {
  public:
   explicit AggregatedHistogramTimerScope(AggregatableHistogramTimer* histogram)