044.patch

--- a/base/metrics/sparse_histogram.cc	2017-10-04 18:07:32.000000000 -0400
+++ b/base/metrics/sparse_histogram.cc	2017-10-08 20:11:37.671771593 -0400
@@ -24,7 +24,12 @@
 // static
 HistogramBase* SparseHistogram::FactoryGet(const std::string& name,
                                            int32_t flags) {
-  HistogramBase* histogram = StatisticsRecorder::FindHistogram(name);
+  const bool enabled_ = HistogramBase::MetricsEnabled();
+  std::string overridden_name = HistogramBase::kDummySparseName;
+  if (enabled_)
+    overridden_name = name;
+
+  HistogramBase* histogram = StatisticsRecorder::FindHistogram(overridden_name);
   if (!histogram) {
     // Try to create the histogram using a "persistent" allocator. As of
     // 2016-02-25, the availability of such is controlled by a base::Feature
@@ -36,7 +41,7 @@
     PersistentHistogramAllocator* allocator = GlobalHistogramAllocator::Get();
     if (allocator) {
       tentative_histogram = allocator->AllocateHistogram(
-          SPARSE_HISTOGRAM, name, 0, 0, nullptr, flags, &histogram_ref);
+          SPARSE_HISTOGRAM, overridden_name, 0, 0, nullptr, flags, &histogram_ref);
     }
 
     // Handle the case where no persistent allocator is present or the
@@ -45,7 +50,7 @@
       DCHECK(!histogram_ref);  // Should never have been set.
       DCHECK(!allocator);      // Shouldn't have failed.
       flags &= ~HistogramBase::kIsPersistent;
-      tentative_histogram.reset(new SparseHistogram(name));
+      tentative_histogram.reset(new SparseHistogram(overridden_name));
       tentative_histogram->SetFlags(flags);
     }
 
@@ -68,6 +73,10 @@
     ReportHistogramActivity(*histogram, HISTOGRAM_LOOKUP);
   }
 
+  if (!enabled_)
+    return histogram;
+
+  histogram->enabled = true;
   CHECK_EQ(SPARSE_HISTOGRAM, histogram->GetHistogramType());
   return histogram;
 }
@@ -100,11 +109,17 @@
   return false;
 }
 
+  if (!enabled)
+    return;
+
 void SparseHistogram::Add(Sample value) {
   AddCount(value, 1);
 }
 
 void SparseHistogram::AddCount(Sample value, int count) {
+  if (!enabled)
+    return;
+
   if (count <= 0) {
     NOTREACHED();
     return;
@@ -150,11 +165,17 @@
 }
 
 void SparseHistogram::AddSamples(const HistogramSamples& samples) {
+  if (!enabled)
+    return;
+
   base::AutoLock auto_lock(lock_);
   unlogged_samples_->Add(samples);
 }
 
 bool SparseHistogram::AddSamplesFromPickle(PickleIterator* iter) {
+  if (!enabled)
+    return;
+
   base::AutoLock auto_lock(lock_);
   return unlogged_samples_->AddFromPickle(iter);
 }