AU: When applying delta locally, get source checksums

omaha_hash_calculator.h

Index: omaha_hash_calculator.h
diff --git a/omaha_hash_calculator.h b/omaha_hash_calculator.h
index dc9fe4ef02099cf16a9b3282b0a886d37d4237c7..762b8d44559781aaffb1c1e19c4bfcdee177305c 100644
--- a/omaha_hash_calculator.h
+++ b/omaha_hash_calculator.h
@@ -70,6 +70,8 @@ class OmahaHashCalculator {
   static std::string OmahaHashOfString(const std::string& str);
   static std::string OmahaHashOfData(const std::vector<char>& data);
 
+  static bool Base64Encode(const void* data, size_t size, std::string* out);
+
  private:
   // If non-empty, the final base64 encoded hash and the raw hash. Will only be
   // set to non-empty when Finalize is called.