Report histogram creation results.

base/metrics/persistent_histogram_allocator.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/metrics/persistent_histogram_allocator.h"
 
 #include "base/lazy_instance.h"
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/metrics/histogram.h"
@@ skipping 161 matching lines @@
 }
 
 // static
 void PersistentHistogramAllocator::SetGlobalAllocator(
     scoped_ptr<PersistentHistogramAllocator> allocator) {
   // Releasing or changing an allocator is extremely dangerous because it
   // likely has histograms stored within it. If the backing memory is also
   // also released, future accesses to those histograms will seg-fault.
   CHECK(!g_allocator);
   g_allocator = allocator.release();
+
+  size_t existing = StatisticsRecorder::GetHistogramCount();
+  DLOG_IF(WARNING, existing)
+      << existing
+      << " histograms were created before persistence was enabled.";
 }
 
 // static
 PersistentHistogramAllocator*
 PersistentHistogramAllocator::GetGlobalAllocator() {
   return g_allocator;
 }
 
 // static
 scoped_ptr<PersistentHistogramAllocator>
@@ skipping 353 matching lines @@
       scoped_ptr<HistogramBase> histogram =
           g_allocator->GetNextHistogramWithIgnore(&iter, last_created);
       if (!histogram)
         break;
       StatisticsRecorder::RegisterOrDeleteDuplicate(histogram.release());
     }
   }
 }
 
 }  // namespace base