Display histograms from subprocesses in chrome://histograms

base/metrics/statistics_recorder.h

 // Copyright (c) 2012 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.
 
 // StatisticsRecorder holds all Histograms and BucketRanges that are used by
 // Histograms in the system. It provides a general place for
 // Histograms/BucketRanges to register, and supports a global API for accessing
 // (i.e., dumping, or graphing) the data.
 
 #ifndef BASE_METRICS_STATISTICS_RECORDER_H_
@@ skipping 15 matching lines @@
 #include "base/metrics/histogram_base.h"
 #include "base/strings/string_piece.h"
 
 namespace base {
 
 class BucketRanges;
 class Lock;
 
 class BASE_EXPORT StatisticsRecorder {
  public:
+  // An interface class for registering objects that can display histograms
+  // on the chrome://histograms page.
+  class MetricsDisplay {

[Ilya Sherman, 2016/04/13 00:29:32]

Optional nit: Perhaps MetricsDisplayer?

[bcwhite, 2016/04/13 11:58:18]

Done.

+   public:
+    // Writes a title string (without formatting) to |output|.
+    virtual void WriteTitleString(std::string* output) = 0;
+
+    // Writes graphs for all known histograms to |output|, optionally with
+    // |html| formatting. If |query| is non-empty, only histograms with
+    // that substring will be included.
+    virtual void WriteGraphs(const std::string& query,
+                             bool html,

[Ilya Sherman, 2016/04/13 00:29:32]

nit: Could you use an enum rather than a bool here, so that callsites are easier
to understand?

[bcwhite, 2016/04/13 11:58:18]

Done.

+                             std::string* output) = 0;
+  };
+
   // A class used as a key for the histogram map below. It always references
   // a string owned outside of this class, likely in the value of the map.
   class StringKey : public StringPiece {
    public:
     // Constructs the StringKey using various sources. The source must live
     // at least as long as the created object.
     StringKey(const std::string& str) : StringPiece(str) {}
     StringKey(StringPiece str) : StringPiece(str) {}
 
     // Though StringPiece is better passed by value than by reference, in
@@ skipping 112 matching lines @@
   static void ClearCallback(const std::string& histogram_name);
 
   // FindCallback retrieves the callback for the histogram referred to by
   // |histogram_name|, or a null callback if no callback exists for this
   // histogram. This method is thread safe.
   static OnSampleCallback FindCallback(const std::string& histogram_name);
 
   // Returns the number of known histograms.
   static size_t GetHistogramCount();
 
+  // Adds an object that can display metrics.
+  static void RegisterMetricsDisplay(MetricsDisplay* display);
+
+  // Removes an object that can display metrics.
+  static void DeregisterMetricsDisplay(MetricsDisplay* display);
+
   // Removes a histogram from the internal set of known ones. This can be
   // necessary during testing persistent histograms where the underlying
   // memory is being released.
   static void ForgetHistogramForTesting(base::StringPiece name);
 
   // Reset any global instance of the statistics-recorder that was created
   // by a call to Initialize().
   static void UninitializeForTesting();
 
  private:
@@ skipping 38 matching lines @@
 
   // Lock protects access to above maps.
   static base::Lock* lock_;
 
   DISALLOW_COPY_AND_ASSIGN(StatisticsRecorder);
 };
 
 }  // namespace base
 
 #endif  // BASE_METRICS_STATISTICS_RECORDER_H_