Alias |ranges| so it appears in minidump.

base/metrics/histogram.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.
 
 // Histogram is an object that aggregates statistics, and can summarize them in
 // various forms, including ASCII graphical, HTML, and numerically (as a
 // vector of numbers corresponding to each of the aggregating buckets).
 // See header file for details and examples.
 
 #include "base/metrics/histogram.h"
@@ skipping 100 matching lines @@
       histogram_type_(histogram_type),
       minimum_(minimum),
       maximum_(maximum),
       bucket_count_(bucket_count),
       flags_(flags) {}
 
   // Create a BucketRanges structure appropriate for this histogram.
   virtual BucketRanges* CreateRanges() {
     BucketRanges* ranges = new BucketRanges(bucket_count_ + 1);
     Histogram::InitializeBucketRanges(minimum_, maximum_, ranges);
+    base::debug::Alias(&ranges);  // TODO(bcwhite): Remove after crbug/586622.

[brucedawson, 2017/08/17 19:28:00]

Be aware that this technique doesn't work very well. Because ranges is a pointer
all that this ensures is that the compiler won't discard the pointer before the
end of the function, which was already guaranteed by the return statement. The
Alias() function does nothing to ensure that the memory pointed to be ranges is
retained in crash dumps. And, either way, the effect of Alias() only extends to
the end of the function where it is called.

See https://chromium-review.googlesource.com/c/619112

[bcwhite, 2017/08/18 05:09:01]

Yeah...  I've noticed that.  :-(  It would be nice if it somehow gave a hint to
Crashpad and got that memory included in a dump.

     return ranges;
   }
 
   // Allocate the correct Histogram object off the heap (in case persistent
   // memory is not available).
   virtual std::unique_ptr<HistogramBase> HeapAlloc(const BucketRanges* ranges) {
     return WrapUnique(new Histogram(name_, minimum_, maximum_, ranges));
   }
 
   // Perform any required datafill on the just-created histogram.  If
@@ skipping 642 matching lines @@
           const DescriptionPair* descriptions)
     : Histogram::Factory(name, LINEAR_HISTOGRAM, minimum, maximum,
                          bucket_count, flags) {
     descriptions_ = descriptions;
   }
 
  protected:
   BucketRanges* CreateRanges() override {
     BucketRanges* ranges = new BucketRanges(bucket_count_ + 1);
     LinearHistogram::InitializeBucketRanges(minimum_, maximum_, ranges);
+    base::debug::Alias(&ranges);  // TODO(bcwhite): Remove after crbug/586622.
     return ranges;
   }
 
   std::unique_ptr<HistogramBase> HeapAlloc(
       const BucketRanges* ranges) override {
     return WrapUnique(new LinearHistogram(name_, minimum_, maximum_, ranges));
   }
 
   void FillHistogram(HistogramBase* base_histogram) override {
     Histogram::Factory::FillHistogram(base_histogram);
@@ skipping 175 matching lines @@
 
 class BooleanHistogram::Factory : public Histogram::Factory {
  public:
   Factory(const std::string& name, int32_t flags)
     : Histogram::Factory(name, BOOLEAN_HISTOGRAM, 1, 2, 3, flags) {}
 
  protected:
   BucketRanges* CreateRanges() override {
     BucketRanges* ranges = new BucketRanges(3 + 1);
     LinearHistogram::InitializeBucketRanges(1, 2, ranges);
+    base::debug::Alias(&ranges);  // TODO(bcwhite): Remove after crbug/586622.
     return ranges;
   }
 
   std::unique_ptr<HistogramBase> HeapAlloc(
       const BucketRanges* ranges) override {
     return WrapUnique(new BooleanHistogram(name_, ranges));
   }
 
  private:
   DISALLOW_COPY_AND_ASSIGN(Factory);
@@ skipping 233 matching lines @@
     Sample sample = custom_ranges[i];
     if (sample < 0 || sample > HistogramBase::kSampleType_MAX - 1)
       return false;
     if (sample != 0)
       has_valid_range = true;
   }
   return has_valid_range;
 }
 
 }  // namespace base