Add the "virtual" keyword on method overrides that are missing it.

chrome/renderer/renderer_histogram_snapshots.h

 // Copyright (c) 2010 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.
 
 #ifndef CHROME_RENDERER_RENDERER_HISTOGRAM_SNAPSHOTS_H_
 #define CHROME_RENDERER_RENDERER_HISTOGRAM_SNAPSHOTS_H_
 #pragma once
 
 #include <map>
 #include <string>
@@ skipping 19 matching lines @@
   typedef std::vector<std::string> HistogramPickledList;
 
   // Extract snapshot data and then send it off the the Browser process.
   // Send only a delta to what we have already sent.
   void UploadAllHistrograms(int sequence_number);
 
   ScopedRunnableMethodFactory<RendererHistogramSnapshots>
       renderer_histogram_snapshots_factory_;
 
   // HistogramSender interface (override) methods.
-  void TransmitHistogramDelta(
+  virtual void TransmitHistogramDelta(
       const base::Histogram& histogram,
       const base::Histogram::SampleSet& snapshot);
-  void InconsistencyDetected(int problem);
-  void UniqueInconsistencyDetected(int problem);
-  void SnapshotProblemResolved(int amount);
+  virtual void InconsistencyDetected(int problem);
+  virtual void UniqueInconsistencyDetected(int problem);
+  virtual void SnapshotProblemResolved(int amount);
 
   // Collection of histograms to send to the browser.
   HistogramPickledList pickled_histograms_;
 
   DISALLOW_COPY_AND_ASSIGN(RendererHistogramSnapshots);
 };
 
 #endif  // CHROME_RENDERER_RENDERER_HISTOGRAM_SNAPSHOTS_H_