First observed in
https://build.chromium.org/p/chromium.memory.fyi/builders/Linux%20Tests%20%28valgrind%29%285%29/builds/40644

r381386 looks culprit.

Leak_DefinitelyLost
48 (32 direct, 16 indirect) bytes in 1 blocks are definitely lost in loss record 6,076 of 11,443
  operator new(unsigned long) (m_replacemalloc/vg_replace_malloc.c:1140)
  base::(anonymous namespace)::CreateRangesFromData(int*, unsigned int, unsigned long) (base/metrics/persistent_histogram_allocator.cc:54)
  base::PersistentHistogramAllocator::CreateHistogram(base::PersistentHistogramAllocator::PersistentHistogramData*) (base/metrics/persistent_histogram_allocator.cc:300)
  base::PersistentHistogramAllocator::GetHistogram(unsigned int) (base/metrics/persistent_histogram_allocator.cc:395)
  base::PersistentHistogramAllocator::GetNextHistogramWithIgnore(base::PersistentHistogramAllocator::Iterator*, unsigned int) (base/metrics/persistent_histogram_allocator.cc:408)
  base::PersistentHistogramAllocator::GetNextHistogram(base::PersistentHistogramAllocator::Iterator*) (/mnt/data/b/build/slave/chromium-rel-linux-valgrind-tests-5/build/src/out/Release/base_unittests)
  base::PersistentHistogramAllocatorTest_CreateAndIterateTest_Test::TestBody() (base/metrics/persistent_histogram_allocator_unittest.cc:114)
Suppression (error hash=#214E65B6549FCE5E#):
  For more info on using suppressions see http://dev.chromium.org/developers/tree-sheriffs/sheriff-details-chromium/memory-sheriff#TOC-Suppressing-memory-reports
{
   <insert_a_suppression_name_here>
   Memcheck:Leak
   fun:_Znw*
   fun:_ZN4base12_GLOBAL__N_120CreateRangesFromDataEPijm
   fun:_ZN4base28PersistentHistogramAllocator15CreateHistogramEPNS0_23PersistentHistogramDataE
   fun:_ZN4base28PersistentHistogramAllocator12GetHistogramEj
   fun:_ZN4base28PersistentHistogramAllocator26GetNextHistogramWithIgnoreEPNS0_8IteratorEj
   fun:_ZN4base28PersistentHistogramAllocator16GetNextHistogramEPNS0_8IteratorE
   fun:_ZN4base58PersistentHistogramAllocatorTest_CreateAndIterateTest_Test8TestBodyEv
}