Display histograms from subprocesses in chrome://histograms

base/metrics/statistics_recorder.h

Index: base/metrics/statistics_recorder.h
diff --git a/base/metrics/statistics_recorder.h b/base/metrics/statistics_recorder.h
index 2fa03f9b2f14664653b5ff6ce62d4626f91eca5b..c1f10c9908839b07b797184cb010dc9ceea7e1cd 100644
--- a/base/metrics/statistics_recorder.h
+++ b/base/metrics/statistics_recorder.h
@@ -33,6 +33,21 @@ 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 {
@@ -165,6 +180,12 @@ class BASE_EXPORT StatisticsRecorder {
   // 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.