Try to detect internal corruption of histogram instances....

chrome/renderer/renderer_histogram_snapshots.cc

 // 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.
 
 #include "chrome/renderer/renderer_histogram_snapshots.h"
 
 #include <ctype.h>
 
 #include "base/logging.h"
 #include "base/message_loop.h"
@@ skipping 34 matching lines @@
     (*it)->SetFlags(Histogram::kIPCSerializationSourceFlag);
     UploadHistrogram(**it, &pickled_histograms);
   }
   // Send the sequence number and list of pickled histograms over synchronous
   // IPC.
   RenderThread::current()->Send(
       new ViewHostMsg_RendererHistograms(
           sequence_number, pickled_histograms));
 }
 
-// Extract snapshot data and then send it off the the Browser process
-// to save it.
+// Extract snapshot data, remember what we've seen so far, and then send off the
+// delta to the browser.
 void RendererHistogramSnapshots::UploadHistrogram(
     const Histogram& histogram,
     HistogramPickledList* pickled_histograms) {
-
   // Get up-to-date snapshot of sample stats.
   Histogram::SampleSet snapshot;
   histogram.SnapshotSample(&snapshot);
   const std::string& histogram_name = histogram.histogram_name();
 
+  int corruption = histogram.FindCorruption(snapshot);
+  if (corruption) {
+    NOTREACHED();
+    // Don't send corrupt data to the browser.
+    UMA_HISTOGRAM_ENUMERATION("Histogram.InconsistenciesRenderer",
+                              corruption, Histogram::NEVER_EXCEEDED_VALUE);
+    typedef std::map<std::string, int> ProblemMap;
+    static ProblemMap* inconsistencies = new ProblemMap;
+    int old_corruption = (*inconsistencies)[histogram_name];
+    if (old_corruption == (corruption | old_corruption))
+      return;  // We've already seen this corruption for this histogram.
+    (*inconsistencies)[histogram_name] |= corruption;
+    UMA_HISTOGRAM_ENUMERATION("Histogram.InconsistenciesRendererUnique",
+                              corruption, Histogram::NEVER_EXCEEDED_VALUE);
+    return;
+  }
+
   // Find the already sent stats, or create an empty set.
   LoggedSampleMap::iterator it = logged_samples_.find(histogram_name);
   Histogram::SampleSet* already_logged;
   if (logged_samples_.end() == it) {
     // Add new entry.
     already_logged = &logged_samples_[histogram.histogram_name()];
     already_logged->Resize(histogram);  // Complete initialization.
   } else {
     already_logged = &(it->second);
     // Deduct any stats we've already logged from our snapshot.
     snapshot.Subtract(*already_logged);
   }
 
   // Snapshot now contains only a delta to what we've already_logged.
 
   if (snapshot.TotalCount() > 0) {
     UploadHistogramDelta(histogram, snapshot, pickled_histograms);
     // Add new data into our running total.
     already_logged->Add(snapshot);
   }
 }
 
 void RendererHistogramSnapshots::UploadHistogramDelta(
     const Histogram& histogram,
     const Histogram::SampleSet& snapshot,
     HistogramPickledList* pickled_histograms) {
-
   DCHECK(0 != snapshot.TotalCount());
   snapshot.CheckSize(histogram);
 
   std::string histogram_info =
       Histogram::SerializeHistogramInfo(histogram, snapshot);
   pickled_histograms->push_back(histogram_info);
 }