Fix a bunch of tiny near-bugs and bugs that static analysis identified...

base/histogram.h

 // Copyright (c) 2006-2008 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).
 
 // It supports calls to accumulate either time intervals (which are processed
 // as integral number of milliseconds), or arbitrary integral units.
@@ skipping 457 matching lines @@
   ThreadSafeHistogram(const char* name, Sample minimum,
                       Sample maximum, size_t bucket_count);
 
   // Provide the analog to Add()
   void Remove(int value);
 
  protected:
   // Provide locked versions to get precise counts.
   virtual void Accumulate(Sample value, Count count, size_t index);
 
-  virtual void SnapshotSample(SampleSet* sample);
+  virtual void SnapshotSample(SampleSet* sample) const;
 
  private:
-  Lock lock_;
+  mutable Lock lock_;
 
   DISALLOW_COPY_AND_ASSIGN(ThreadSafeHistogram);
 };
 
 //------------------------------------------------------------------------------
 // StatisticsRecorder handles all histograms in the system.  It provides a
 // general place for histograms to register, and supports a global API for
 // accessing (i.e., dumping, or graphing) the data in all the histograms.
 
 class StatisticsRecorder {
@@ skipping 42 matching lines @@
   // lock protects access to the above map.
   static Lock* lock_;
 
   // Dump all known histograms to log.
   static bool dump_on_exit_;
 
   DISALLOW_COPY_AND_ASSIGN(StatisticsRecorder);
 };
 
 #endif  // BASE_HISTOGRAM_H__