Report histogram creation results.

base/metrics/histogram_base.cc

Index: base/metrics/histogram_base.cc
diff --git a/base/metrics/histogram_base.cc b/base/metrics/histogram_base.cc
index 3a40e6813fc6f5c7669c627e4bbc007e6d7184d3..c4c3ed24172dd29d660149d4216193144d513316 100644
--- a/base/metrics/histogram_base.cc
+++ b/base/metrics/histogram_base.cc
@@ -62,6 +62,7 @@ HistogramBase* DeserializeHistogramInfo(PickleIterator* iter) {
 }
 
 const HistogramBase::Sample HistogramBase::kSampleType_MAX = INT_MAX;
+HistogramBase* HistogramBase::report_histogram_ = nullptr;
 
 HistogramBase::HistogramBase(const std::string& name)
     : histogram_name_(name),
@@ -122,6 +123,30 @@ void HistogramBase::WriteJSON(std::string* output) const {
   serializer.Serialize(root);
 }
 
+// static
+void HistogramBase::EnableActivityReportHistogram(
+    const std::string& process_type) {
+  DCHECK(!report_histogram_);
+  size_t existing = StatisticsRecorder::GetHistogramCount();
+  if (existing != 0) {
+    DLOG(WARNING) << existing
+                  << " histograms were created before reporting was enabled.";
+  }
+
+  std::string name =
+      "UMA." + (process_type.empty() ? process_type : process_type + ".") +
+      "Histograms.Activity";
+
+  // Calling FactoryGet() here rather than using a histogram-macro works
+  // around some problems with tests that could end up seeing the results
+  // histogram when not expected due to a bad interaction between
+  // HistogramTester and StatisticsRecorder.
+  report_histogram_ = LinearHistogram::FactoryGet(
+      name, 1, HISTOGRAM_REPORT_MAX, HISTOGRAM_REPORT_MAX + 1,
+      kUmaTargetedHistogramFlag);
+  report_histogram_->Add(HISTOGRAM_REPORT_CREATED);
+}
+
 void HistogramBase::FindAndRunCallback(HistogramBase::Sample sample) const {
   if ((flags() & kCallbackExists) == 0)
     return;
@@ -163,4 +188,54 @@ void HistogramBase::WriteAsciiBucketValue(Count current,
   StringAppendF(output, " (%d = %3.1f%%)", current, current/scaled_sum);
 }
 
+// static
+void HistogramBase::ReportHistogramActivity(HistogramBase* histogram,

[Alexei Svitkine (slow), 2016/03/07 21:14:51]

This param can be const. And in fact you might as well pass it by const ref
since the param shouldn't be null.

[bcwhite, 2016/03/07 22:20:41]

Done.

+                                            ReportActivity activity) {
+  if (!report_histogram_)
+    return;
+
+  const int32_t flags = histogram->flags_;
+  HistogramReport report_type;
+  switch (activity) {
+    case HISTOGRAM_CREATED:
+      report_histogram_->Add(HISTOGRAM_REPORT_HISTOGRAM_CREATED);
+      switch (histogram->GetHistogramType()) {
+        case HISTOGRAM:
+          report_type = HISTOGRAM_REPORT_TYPE_LOGARITHMIC;
+          break;
+        case LINEAR_HISTOGRAM:
+          report_type = HISTOGRAM_REPORT_TYPE_LINEAR;
+          break;
+        case BOOLEAN_HISTOGRAM:
+          report_type = HISTOGRAM_REPORT_TYPE_BOOLEAN;
+          break;
+        case CUSTOM_HISTOGRAM:
+          report_type = HISTOGRAM_REPORT_TYPE_CUSTOM;
+          break;
+        case SPARSE_HISTOGRAM:
+          report_type = HISTOGRAM_REPORT_TYPE_SPARSE;
+          break;
+        default:

[Alexei Svitkine (slow), 2016/03/07 21:14:51]

No need for default case. GetHistogramType() return value is HistogramType which
compilers will validate against the switch and produce a compile error when a
case isn't handled.

Same thing for the ReportActivity switch.

[bcwhite, 2016/03/07 22:20:41]

The Windows compiler does not produce such an error.  I tried omitting both
"dafault" and SPARSE_HISTOGRAM from the switch and no error, debug or release.

Also, without the "default" case, is reports a potentially uninitialized
variable in "report_type".

I can omit the default and initialize report_type to HISTOGRAM_REPORT_MAX if
other compilers will indeed fail.

[Alexei Svitkine (slow), 2016/03/08 19:55:30]

Other platforms do - specifically clang. Since this is a cross-platform file,
having one platform warn is sufficient, so omitting default and initializing the
var SGTM.

Omit the default in the outer switch too, please. Thanks.

[bcwhite, 2016/03/09 01:57:26]

Cool.  I thought that was the case but was playing it safe.  Done.  Also applies
to HistogramTypeToString, above.

+          NOTREACHED();
+          report_type = HISTOGRAM_REPORT_MAX;
+          break;
+      }
+      report_histogram_->Add(report_type);
+      if (flags & kIsPersistent)
+        report_histogram_->Add(HISTOGRAM_REPORT_FLAG_PERSISTENT);
+      if (flags & (kUmaStabilityHistogramFlag & ~kUmaTargetedHistogramFlag))
+        report_histogram_->Add(HISTOGRAM_REPORT_FLAG_UMA_STABILITY);
+      else if (flags & kUmaTargetedHistogramFlag)
+        report_histogram_->Add(HISTOGRAM_REPORT_FLAG_UMA_TARGETED);
+      break;
+
+    case HISTOGRAM_LOOKUP:
+      report_histogram_->Add(HISTOGRAM_REPORT_HISTOGRAM_LOOKUP);
+      break;
+
+    default:
+      NOTREACHED();
+  }
+}
+
 }  // namespace base