Support "shared" histograms between processes.

base/metrics/statistics_recorder.cc

Index: base/metrics/statistics_recorder.cc
diff --git a/base/metrics/statistics_recorder.cc b/base/metrics/statistics_recorder.cc
index 84ebbc58dbc37fb7724180b34d157b22021ae222..5553a5681a23480d90330d3ca558b942e05dae62 100644
--- a/base/metrics/statistics_recorder.cc
+++ b/base/metrics/statistics_recorder.cc
@@ -24,6 +24,22 @@ base::LazyInstance<base::StatisticsRecorder>::Leaky g_statistics_recorder_ =
 
 namespace base {
 
+StatisticsRecorder::HistogramIterator&
+StatisticsRecorder::HistogramIterator::operator++() {
+  const HistogramMap::iterator histograms_end = histograms_->end();
+  while (iter_ != histograms_end) {
+    ++iter_;
+    if (iter_ == histograms_end)
+      break;
+    if (!include_persistent_ && (iter_->second->flags() &
+                                 HistogramBase::kIsPersistent)) {
+      continue;
+    }
+    break;
+  }
+  return *this;
+}
+
 // static
 void StatisticsRecorder::Initialize() {
   // Ensure that an instance of the StatisticsRecorder object is created.
@@ -59,10 +75,10 @@ HistogramBase* StatisticsRecorder::RegisterOrDeleteDuplicate(
       histogram_to_return = histogram;
     } else {
       const std::string& name = histogram->histogram_name();
-      uint64_t id = histogram->name_hash();
-      HistogramMap::iterator it = histograms_->find(id);
+      uint64_t hash = histogram->name_hash();
+      HistogramMap::iterator it = histograms_->find(hash);
       if (histograms_->end() == it) {
-        (*histograms_)[id] = histogram;
+        (*histograms_)[hash] = histogram;
         ANNOTATE_LEAKING_OBJECT_PTR(histogram);  // see crbug.com/79322
         // If there are callbacks for this histogram, we set the kCallbackExists
         // flag.
@@ -296,7 +312,18 @@ StatisticsRecorder::OnSampleCallback StatisticsRecorder::FindCallback(
                                                 : OnSampleCallback();
 }
 
-// private static
+// static
+StatisticsRecorder::HistogramIterator StatisticsRecorder::begin(
+    bool include_persistent) {
+  return HistogramIterator(histograms_->begin(), include_persistent);
+}
+
+// static
+StatisticsRecorder::HistogramIterator StatisticsRecorder::end() {
+  return HistogramIterator(histograms_->end(), true);
+}
+
+// static
 void StatisticsRecorder::GetSnapshot(const std::string& query,
                                      Histograms* snapshot) {
   if (lock_ == NULL)