Remove static locals from histograms.

webrtc/system_wrappers/source/metrics_default.cc

Index: webrtc/system_wrappers/source/metrics_default.cc
diff --git a/webrtc/system_wrappers/source/metrics_default.cc b/webrtc/system_wrappers/source/metrics_default.cc
index 6ca90dafdc84933c8805f0f550809c1ceb36fe66..e1e4e807b3487ffe9902b63329ab498ea7c121e9 100644
--- a/webrtc/system_wrappers/source/metrics_default.cc
+++ b/webrtc/system_wrappers/source/metrics_default.cc
@@ -253,6 +253,18 @@ const std::string& GetHistogramName(Histogram* histogram_pointer) {
 
 // Fast path. Adds |sample| to cached |histogram_pointer|.
 void HistogramAdd(Histogram* histogram_pointer, int sample) {
+  if (g_rtc_histogram_map == nullptr) {
+    // Histograms are disabled, so the pointer is invalid. Check on this instead
+    // of histogram_pointer being NULL so that we don't accidentally miss
+    // instances where HistogramAdd(histogram_, sample) is called with
+    // histogram_ uninitialized.
+    //
+    // This doesn't happen in Chromium since base::Histogram::FactoryGet and
+    // base::LinearHistogram::FactoryGet always return valid base::HistogramBase
+    // pointers. We could consider returning a null object, but having
+    // RtcHistogram virtual makes function calls to it slower.
+    return;
+  }
   RtcHistogram* ptr = reinterpret_cast<RtcHistogram*>(histogram_pointer);
   ptr->Add(sample);
 }
@@ -267,6 +279,8 @@ SampleInfo::~SampleInfo() {}
 
 // Implementation of global functions in metrics_default.h.
 void Enable() {
+  // TODO(pbos): Make sure that no callers have called HistogramFactoryGet*,
+  // HistogramAdd or GetMap() at this point.
   RTC_DCHECK(g_rtc_histogram_map == nullptr);
 #if RTC_DCHECK_IS_ON
   RTC_DCHECK_EQ(0, rtc::AtomicOps::AcquireLoad(&g_rtc_histogram_called));