Persist setup metrics and have Chrome report them during UMA upload.

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 55 matching lines @@
 // 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);
-  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;
 }
 
 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 72 matching lines @@
 }
 
 SampleCountIterator::~SampleCountIterator() {}
 
 bool SampleCountIterator::GetBucketIndex(size_t* index) const {
   DCHECK(!Done());
   return false;
 }
 
 }  // namespace base