NOT YET READY: UMA recording the kind of target frame when extensions pierce browsing instance.

base/test/histogram_tester.h

 // Copyright 2014 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.
 
 #ifndef BASE_TEST_HISTOGRAM_TESTER_H_
 #define BASE_TEST_HISTOGRAM_TESTER_H_
 
 #include <map>
 #include <memory>
 #include <ostream>
 #include <string>
 #include <utility>
 #include <vector>
 
 #include "base/macros.h"
 #include "base/metrics/histogram.h"
 #include "base/metrics/histogram_base.h"
 #include "base/time/time.h"
 
 namespace base {
 
 struct Bucket;
 class HistogramSamples;
 
 // HistogramTester provides a simple interface for examining histograms, UMA
 // or otherwise. Tests can use this interface to verify that histogram data is
 // getting logged as intended.
+//
+// Note: When using this class from a browser test, one might have to call
+// SubprocessMetricsProvider::MergeHistogramDeltasForTesting() to sync the
+// histogram data between the renderer and browser processes.
 class HistogramTester {
  public:
   using CountsMap = std::map<std::string, HistogramBase::Count>;
 
   // The constructor will call StatisticsRecorder::Initialize() for you. Also,
   // this takes a snapshot of all current histograms counts.
   HistogramTester();
   ~HistogramTester();
 
   // We know the exact number of samples in a bucket, and that no other bucket
@@ skipping 108 matching lines @@
 
   HistogramBase::Sample min;
   HistogramBase::Count count;
 };
 
 void PrintTo(const Bucket& value, std::ostream* os);
 
 }  // namespace base
 
 #endif  // BASE_TEST_HISTOGRAM_TESTER_H_