Add construction checksum to safe-browsing's BloomFilter.

chrome/browser/safe_browsing/bloom_filter.h

Index: chrome/browser/safe_browsing/bloom_filter.h
diff --git a/chrome/browser/safe_browsing/bloom_filter.h b/chrome/browser/safe_browsing/bloom_filter.h
index 9730ffda9b006574059018ca6f34ba1a744ade42..5a1e6ef9a646ef920215bc6d54c4d460775b536e 100644
--- a/chrome/browser/safe_browsing/bloom_filter.h
+++ b/chrome/browser/safe_browsing/bloom_filter.h
@@ -66,6 +66,10 @@ class BloomFilter : public base::RefCountedThreadSafe<BloomFilter> {
   // tests wish to make their own calculations.
   static int FilterSizeForKeyCount(int key_count);
 
+  // Check whether the contents of the bloom filter have changed since
+  // construction.  Present while debugging PrefixSet.
+  bool CheckChecksum() const;
+
  private:
   friend class base::RefCountedThreadSafe<BloomFilter>;
   FRIEND_TEST_ALL_PREFIXES(SafeBrowsingBloomFilter, BloomFilterUse);
@@ -102,6 +106,10 @@ class BloomFilter : public base::RefCountedThreadSafe<BloomFilter> {
   // Random keys used for hashing.
   HashKeys hash_keys_;
 
+  // For debugging, used to verify that |hash_keys_| and |data_| have
+  // not changed other than via constructor or Insert().
+  uint32 checksum_;
+
   DISALLOW_COPY_AND_ASSIGN(BloomFilter);
 };