Display histograms from subprocesses in chrome://histograms

base/metrics/sparse_histogram.h

Index: base/metrics/sparse_histogram.h
diff --git a/base/metrics/sparse_histogram.h b/base/metrics/sparse_histogram.h
index 3b302d6f223f626cfa8f152048a08af8e1b9f1d5..b9b012c984b9201b875e4b53081e4c68e3bc802c 100644
--- a/base/metrics/sparse_histogram.h
+++ b/base/metrics/sparse_histogram.h
@@ -82,8 +82,10 @@ class BASE_EXPORT SparseHistogram : public HistogramBase {
   std::unique_ptr<HistogramSamples> SnapshotSamples() const override;
   std::unique_ptr<HistogramSamples> SnapshotDelta() override;
   std::unique_ptr<HistogramSamples> SnapshotFinalDelta() const override;
-  void WriteHTMLGraph(std::string* output) const override;
-  void WriteAscii(std::string* output) const override;
+  void WriteHTMLGraph(const HistogramSamples* snapshot,
+                      std::string* output) const override;
+  void WriteAscii(const HistogramSamples* snapshot,
+                  std::string* output) const override;
 
  protected:
   // HistogramBase implementation:
@@ -110,6 +112,7 @@ class BASE_EXPORT SparseHistogram : public HistogramBase {
   // Helpers for emitting Ascii graphic.  Each method appends data to output.
   void WriteAsciiImpl(bool graph_it,
                       const std::string& newline,
+                      const HistogramSamples* snapshot,
                       std::string* output) const;
 
   // Write a common header message describing this histogram.