Remove typically unused local_metadata_ field.

base/metrics/histogram_samples.cc

 // Copyright (c) 2012 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/histogram_samples.h"
 
 #include <limits>
 
 #include "base/compiler_specific.h"
 #include "base/numerics/safe_conversions.h"
@@ skipping 146 matching lines @@
 bool HistogramSamples::AtomicSingleSample::IsDisabled() const {
   return subtle::Acquire_Load(&as_atomic) == kDisabledSingleSample;
 }
 
 HistogramSamples::LocalMetadata::LocalMetadata() {
   // This is the same way it's done for persistent metadata since no ctor
   // is called for the data members in that case.
   memset(this, 0, sizeof(*this));
 }
 
-// Don't try to delegate behavior to the constructor below that accepts a
-// Matadata pointer by passing &local_meta_. Such cannot be reliably passed
-// because it has not yet been constructed -- no member variables have; the
-// class itself is in the middle of being constructed. Using it to
-// initialize meta_ is okay because the object now exists and local_meta_
-// is before meta_ in the construction order.
-HistogramSamples::HistogramSamples(uint64_t id)
-    : meta_(&local_meta_) {
-  meta_->id = id;
-}
-
 HistogramSamples::HistogramSamples(uint64_t id, Metadata* meta)
     : meta_(meta) {
   DCHECK(meta_->id == 0 || meta_->id == id);
 
   // It's possible that |meta| is contained in initialized, read-only memory
   // so it's essential that no write be done in that case.
   if (!meta_->id)
     meta_->id = id;
 }
 
+// This mustn't do anything with |meta_|. It was passed to the ctor and may
+// be invalid by the time this dtor gets called.
 HistogramSamples::~HistogramSamples() {}
 
 void HistogramSamples::Add(const HistogramSamples& other) {
   IncreaseSumAndCount(other.sum(), other.redundant_count());
   std::unique_ptr<SampleCountIterator> it = other.Iterator();
   bool success = AddSubtractImpl(it.get(), ADD);
   DCHECK(success);
 }
 
 bool HistogramSamples::AddFromPickle(PickleIterator* iter) {
@@ skipping 100 matching lines @@
 
 bool SingleSampleIterator::GetBucketIndex(size_t* index) const {
   DCHECK(!Done());
   if (bucket_index_ == kSizeMax)
     return false;
   *index = bucket_index_;
   return true;
 }
 
 }  // namespace base