Don't use a delgating constructor passing a member variable.

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 "base/compiler_specific.h"
 #include "base/pickle.h"
 
 namespace base {
@@ skipping 41 matching lines @@
                                     HistogramBase::Sample* max,
                                     HistogramBase::Count* count) const {
   DCHECK(!Done());
   *min = min_;
   *max = max_;
   *count = count_;
 }
 
 }  // namespace
 
+// Don't try to delegate behavior to the constructor below that accepts a
+// Matadata pointer by passing &local_meta_. Such cannot be reliably passed

[Nico, 2015/12/14 20:49:01]

typo matadata

+// 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)
-    : HistogramSamples(id, &local_meta_) {}
+    : meta_(&local_meta_) {
+  meta_->id = id;
+}
 
 HistogramSamples::HistogramSamples(uint64_t id, Metadata* meta)
     : meta_(meta) {
   DCHECK(meta_->id == 0 || meta_->id == id);

[Alexei Svitkine (slow), 2015/12/14 18:54:41]

Nit: Add this line to the ctor above.

[bcwhite, 2015/12/14 19:11:07]

Unnecessary since local_meta_ has just been constructed and is guaranteed to
have an default id of zero.

   meta_->id = id;
 }
 
 HistogramSamples::~HistogramSamples() {}
 
 // Despite using atomic operations, the increment/add actions below are *not*
 // atomic! Race conditions may cause loss of samples or even completely corrupt
 // the 64-bit sum on 32-bit machines. This is done intentionally to reduce the
 // cost of these operations that could be executed in performance-significant
 //  points of the code.
@@ skipping 73 matching lines @@
 }
 
 SampleCountIterator::~SampleCountIterator() {}
 
 bool SampleCountIterator::GetBucketIndex(size_t* index) const {
   DCHECK(!Done());
   return false;
 }
 
 }  // namespace base