Display histograms from subprocesses in chrome://histograms

base/metrics/histogram.cc

Index: base/metrics/histogram.cc
diff --git a/base/metrics/histogram.cc b/base/metrics/histogram.cc
index 86c6746c0f590199cefe57c21d35ed4fcb7bd3a2..231e9379ac0d61bf8a42738edc3760cca66f0745 100644
--- a/base/metrics/histogram.cc
+++ b/base/metrics/histogram.cc
@@ -462,15 +462,19 @@ bool Histogram::AddSamplesFromPickle(PickleIterator* iter) {
 }
 
 // The following methods provide a graphical histogram display.
-void Histogram::WriteHTMLGraph(std::string* output) const {
+void Histogram::WriteHTMLGraph(const HistogramSamples* snapshot,
+                               std::string* output) const {
   // TBD(jar) Write a nice HTML bar chart, with divs an mouse-overs etc.
   output->append("<PRE>");
-  WriteAsciiImpl(true, "<br>", output);
+  WriteAsciiImpl(true, "<br>", static_cast<const SampleVector*>(snapshot),

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

Hmm, I'm not super happy about the static_cast here.  Why is it needed?  That
is, could either this method accept a SampleVector, or the WriteAsciiImpl method
accept a HistogramSamples param?

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

This is a virtual function off of HistogramBase so has to use the
HistogramSamples base class there (or it won't work with SparseHistogram).

I originally tried passing HistogramSamples all the way but WriteAsciiImpl needs
to call methods defined in (and only applicable to) SampleVector.

I could pass HistogramSamples to WriteAsciiImpl and do the static_cast in there
but that made for slightly more complicated code.  It seemed more clear to do
the cast in the overridden method.

+                 output);
   output->append("</PRE>");
 }
 
-void Histogram::WriteAscii(std::string* output) const {
-  WriteAsciiImpl(true, "\n", output);
+void Histogram::WriteAscii(const HistogramSamples* snapshot,
+                           std::string* output) const {
+  WriteAsciiImpl(true, "\n", static_cast<const SampleVector*>(snapshot),
+                 output);
 }
 
 bool Histogram::SerializeInfoImpl(Pickle* pickle) const {
@@ -578,10 +582,15 @@ std::unique_ptr<SampleVector> Histogram::SnapshotSampleVector() const {
 
 void Histogram::WriteAsciiImpl(bool graph_it,
                                const std::string& newline,
+                               const SampleVector* snapshot,
                                std::string* output) const {
   // Get local (stack) copies of all effectively volatile class data so that we
   // are consistent across our output activities.

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

nit: Mebbe move this comment into the if-stmt?

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

Done.

-  std::unique_ptr<SampleVector> snapshot = SnapshotSampleVector();
+  std::unique_ptr<SampleVector> local_snapshot;
+  if (!snapshot) {
+    local_snapshot = SnapshotSampleVector();
+    snapshot = local_snapshot.get();
+  }
   Count sample_count = snapshot->TotalCount();
 
   WriteAsciiHeader(*snapshot, sample_count, output);