Add TraceAnalyzer support for calculating common event rate statistics

base/test/trace_event_analyzer.h

Index: base/test/trace_event_analyzer.h
diff --git a/base/test/trace_event_analyzer.h b/base/test/trace_event_analyzer.h
index d41cff2ec0bc1ce1c34184a5ddcb7758bc98e7ab..b81b8ed3d049de757c99082ca3aa19257190ce44 100644
--- a/base/test/trace_event_analyzer.h
+++ b/base/test/trace_event_analyzer.h
@@ -411,6 +411,13 @@ class TraceAnalyzer {
  public:
   typedef std::vector<const TraceEvent*> TraceEventVector;
 
+  struct Stats {
+    double min_us;
+    double max_us;
+    double mean_us;
+    double standard_deviation_us;
+  };
+
   ~TraceAnalyzer();
 
   // Use trace events from JSON string generated by tracing API.
@@ -461,6 +468,10 @@ class TraceAnalyzer {
 
   const std::string& GetThreadName(const TraceEvent::ProcessThreadID& thread);
 
+  // Calculate min/max/mean and standard deviation from the times between
+  // adjacent events.
+  static bool GetRateStats(const TraceEventVector& events, Stats* stats);
+
  private:
   TraceAnalyzer();