Instrument to catch corruption constructing safe-browsing filters.

chrome/browser/safe_browsing/prefix_set.h

Index: chrome/browser/safe_browsing/prefix_set.h
diff --git a/chrome/browser/safe_browsing/prefix_set.h b/chrome/browser/safe_browsing/prefix_set.h
index 91fe7fb4957f41ade2ab2fbf34fc22cf4970c6cb..abecbd91e914e47bd84d77f3222c62dcdb92726c 100644
--- a/chrome/browser/safe_browsing/prefix_set.h
+++ b/chrome/browser/safe_browsing/prefix_set.h
@@ -89,10 +89,14 @@ class PrefixSet {
   // |target_index|.  Only call if |IsDeltaAt()| returned |true|.
   uint16 DeltaAt(size_t target_index) const;
 
-  // Check whether |index_| and |deltas_| still match the CRC
+  // Check whether |index_| and |deltas_| still match the checksum
   // generated during construction.
   bool CheckChecksum() const;
 
+  // Accumulates xor checksum over what GetPrefixes() would return,
+  // without requiring a large temporary structure.
+  SBPrefix GetPrefixesChecksum() const;
+
  private:
   // Maximum number of consecutive deltas to encode before generating
   // a new index entry.  This helps keep the worst-case performance