Crash when we notice a corruption of the histogram range-vector...

base/metrics/histogram.h

Index: base/metrics/histogram.h
===================================================================
--- base/metrics/histogram.h	(revision 75929)
+++ base/metrics/histogram.h	(working copy)
@@ -411,7 +411,7 @@
   Sample declared_min() const { return declared_min_; }
   Sample declared_max() const { return declared_max_; }
   virtual Sample ranges(size_t i) const;
-  Sample range_checksum() const { return range_checksum_; }
+  uint32 range_checksum() const { return range_checksum_; }
   virtual size_t bucket_count() const;
   // Snapshot the current complete set of sample data.
   // Override with atomic/locked snapshot if needed.
@@ -473,6 +473,8 @@
   // Allow tests to corrupt our innards for testing purposes.
   FRIEND_TEST(HistogramTest, CorruptBucketBounds);
   FRIEND_TEST(HistogramTest, CorruptSampleCounts);
+  FRIEND_TEST(HistogramTest, Crc32SampleHash);
+  FRIEND_TEST(HistogramTest, Crc32TableTest);
 
   // Post constructor initialization.
   void Initialize();
@@ -480,8 +482,11 @@
   // Return true iff the range_checksum_ matches current ranges_ vector.
   bool HasValidRangeChecksum() const;
 
-  Sample CalculateRangeChecksum() const;
+  uint32 CalculateRangeChecksum() const;
 
+  // Checksum function for accumulating range values into a checksum.
+  static uint32 Crc32(uint32 sum, Sample range);
+
   //----------------------------------------------------------------------------
   // Helpers for emitting Ascii graphic.  Each method appends data to output.
 
@@ -508,6 +513,9 @@
                              std::string* output) const;
 
   //----------------------------------------------------------------------------
+  // Table for generating Crc32 values.
+  static const uint32 kCrcTable[256];
+  //----------------------------------------------------------------------------
   // Invariant values set at/near construction time
 
   // ASCII version of original name given to the constructor.  All identically
@@ -526,10 +534,10 @@
   // The dimension of ranges_ is bucket_count + 1.
   Ranges ranges_;
 
-  // For redundancy, we store the sum of all the sample ranges when ranges are
-  // generated.  If ever there is ever a difference, then the histogram must
+  // For redundancy, we store a checksum of all the sample ranges when ranges
+  // are generated.  If ever there is ever a difference, then the histogram must
   // have been corrupted.
-  Sample range_checksum_;
+  uint32 range_checksum_;
 
   // Finally, provide the state that changes with the addition of each new
   // sample.