Break global impact of PersistentHistogramAllocator into a separate class.

base/metrics/sparse_histogram.cc

Index: base/metrics/sparse_histogram.cc
diff --git a/base/metrics/sparse_histogram.cc b/base/metrics/sparse_histogram.cc
index 1118c4149ef95f6c8e734ef7fca3646b58b8c50c..31fcfd93d63cc4d1ee14667433488510785da7ad 100644
--- a/base/metrics/sparse_histogram.cc
+++ b/base/metrics/sparse_histogram.cc
@@ -24,12 +24,6 @@ typedef HistogramBase::Sample Sample;
 // static
 HistogramBase* SparseHistogram::FactoryGet(const std::string& name,
                                            int32_t flags) {
-  // Import histograms from known persistent storage. Histograms could have
-  // been added by other processes and they must be fetched and recognized
-  // locally in order to be found by FindHistograms() below. If the persistent
-  // memory segment is not shared between processes, this call does nothing.
-  PersistentHistogramAllocator::ImportGlobalHistograms();
-
   HistogramBase* histogram = StatisticsRecorder::FindHistogram(name);
   if (!histogram) {
     // Try to create the histogram using a "persistent" allocator. As of
@@ -39,8 +33,7 @@ HistogramBase* SparseHistogram::FactoryGet(const std::string& name,
     // the process heap.
     PersistentMemoryAllocator::Reference histogram_ref = 0;
     std::unique_ptr<HistogramBase> tentative_histogram;
-    PersistentHistogramAllocator* allocator =
-        PersistentHistogramAllocator::GetGlobalAllocator();
+    PersistentHistogramAllocator* allocator = GlobalHistogramAllocator::Get();
     if (allocator) {
       tentative_histogram = allocator->AllocateHistogram(
           SPARSE_HISTOGRAM, name, 0, 0, nullptr, flags, &histogram_ref);