Add TraceAnalyzer support for calculating common event rate statistics

base/test/trace_event_analyzer.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Use trace_analyzer::Query and trace_analyzer::TraceAnalyzer to search for
 // specific trace events that were generated by the trace_event.h API.
 //
 // Basic procedure:
 // - Get trace events JSON string from base::debug::TraceLog.
 // - Create TraceAnalyzer with JSON string.
@@ skipping 393 matching lines @@
   ~QueryNode();
 
   Query query_;
 };
 
 // TraceAnalyzer helps tests search for trace events.
 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.
   // Returns non-NULL if the JSON is successfully parsed.
   static TraceAnalyzer* Create(const std::string& json_events)
                                WARN_UNUSED_RESULT;
 
   // Associate BEGIN and END events with each other. This allows Query(OTHER_*)
   // to access the associated event and enables Query(EVENT_DURATION).
   // An end event will match the most recent begin event with the same name,
@@ skipping 30 matching lines @@
                        const Query& match);
 
   // Find all events that match query and replace output vector.
   size_t FindEvents(const Query& query, TraceEventVector* output);
 
   // Helper method: find first event that matches query
   const TraceEvent* FindOneEvent(const Query& query);
 
   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();
 
   bool SetEvents(const std::string& json_events) WARN_UNUSED_RESULT;
 
   // Read metadata (thread names, etc) from events.
   void ParseMetadata();
 
   std::map<TraceEvent::ProcessThreadID, std::string> thread_names_;
   std::vector<TraceEvent> raw_events_;
   bool allow_assocation_changes_;
 
   DISALLOW_COPY_AND_ASSIGN(TraceAnalyzer);
 };
 
 }  // namespace trace_analyzer
 
 #endif  // BASE_TEST_TRACE_EVENT_ANALYZER_H_