Remove typically unused local_metadata_ field.

base/metrics/sample_map.cc

Index: base/metrics/sample_map.cc
diff --git a/base/metrics/sample_map.cc b/base/metrics/sample_map.cc
index f0e4e5edb15b089394dfa95fe57ce106ca9d5266..08fe032057702df2f4f500f836891a843a8a007a 100644
--- a/base/metrics/sample_map.cc
+++ b/base/metrics/sample_map.cc
@@ -79,9 +79,11 @@ void SampleMapIterator::SkipEmptyBuckets() {
 
 SampleMap::SampleMap() : SampleMap(0) {}
 
-SampleMap::SampleMap(uint64_t id) : HistogramSamples(id) {}
+SampleMap::SampleMap(uint64_t id) : HistogramSamples(id, new LocalMetadata()) {}
 
-SampleMap::~SampleMap() {}
+SampleMap::~SampleMap() {
+  delete static_cast<LocalMetadata*>(meta());
+}
 
 void SampleMap::Accumulate(Sample value, Count count) {
   sample_counts_[value] += count;