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 3571657513f6482c5724f721c17e8a2c354ab79a..8af73e91d098e2e753a775b870d39c7d1208d44e 100644
--- a/base/metrics/histogram.cc
+++ b/base/metrics/histogram.cc
@@ -476,15 +476,19 @@ 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),
+                 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 {
@@ -592,10 +596,15 @@ 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.
-  std::unique_ptr<SampleVector> snapshot = SnapshotSampleVector();
+  std::unique_ptr<SampleVector> local_snapshot;
+  if (!snapshot) {
+    // Get local (stack) copies of all effectively volatile class data so
+    // that we are consistent across our output activities.
+    local_snapshot = SnapshotSampleVector();
+    snapshot = local_snapshot.get();
+  }
   Count sample_count = snapshot->TotalCount();
 
   WriteAsciiHeader(*snapshot, sample_count, output);