Fix StatisticsRecorder to handle re-entry during tests.

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 d0fa2add3603b3f574dfa9ef9e5ee2e6b152aafc..9b3ad2643cfb7986e1f9fc657c53b242422c9835 100644
--- a/base/metrics/statistics_recorder.cc
+++ b/base/metrics/statistics_recorder.cc
@@ -369,12 +369,6 @@ StatisticsRecorder::OnSampleCallback StatisticsRecorder::FindCallback(
 }
 
 // static
-void StatisticsRecorder::ResetForTesting() {
-  // Just call the private version that is used also by the destructor.
-  Reset();
-}
-
-// static
 void StatisticsRecorder::ForgetHistogramForTesting(base::StringPiece name) {
   if (histograms_)
     histograms_->erase(HashMetricName(name.as_string()));
@@ -384,7 +378,6 @@ void StatisticsRecorder::ForgetHistogramForTesting(base::StringPiece name) {
 // of main(), and hence it is not thread safe.  It initializes globals to
 // provide support for all future calls.
 StatisticsRecorder::StatisticsRecorder() {
-  DCHECK(!histograms_);
   if (lock_ == NULL) {
     // This will leak on purpose. It's the only way to make sure we won't race
     // against the static uninitialization of the module while one of our
@@ -394,7 +387,13 @@ StatisticsRecorder::StatisticsRecorder() {
     // during static initialization and released only on  process termination.
     lock_ = new base::Lock;
   }
+
   base::AutoLock auto_lock(*lock_);
+
+  existing_histograms_.reset(histograms_);
+  existing_callbacks_.reset(callbacks_);
+  existing_ranges_.reset(ranges_);
+
   histograms_ = new HistogramMap;
   callbacks_ = new CallbackMap;
   ranges_ = new RangesMap;
@@ -406,8 +405,12 @@ StatisticsRecorder::StatisticsRecorder() {
 StatisticsRecorder::~StatisticsRecorder() {
   DCHECK(histograms_ && ranges_ && lock_);
 
-  // Global clean up.
+  // Clean out what this object created and then restore what existed before.
   Reset();
+  base::AutoLock auto_lock(*lock_);
+  histograms_ = existing_histograms_.release();
+  callbacks_ = existing_callbacks_.release();
+  ranges_ = existing_ranges_.release();
 }
 
 // static