base::MD5IntermediateFinal() generates digest non-destructively.

base/md5.h

Index: base/md5.h
diff --git a/base/md5.h b/base/md5.h
index fba02bd11635d63ac2057e25cf150bc25d84f012..0a87fcf7c4aa56c1ed6eaece425a6e49a71735c7 100644
--- a/base/md5.h
+++ b/base/md5.h
@@ -58,6 +58,12 @@ BASE_EXPORT void MD5Update(MD5Context* context, const StringPiece& data);
 // Finalizes the MD5 operation and fills the buffer with the digest.
 BASE_EXPORT void MD5Final(MD5Digest* digest, MD5Context* context);
 
+// MD5IntermediateFinal() generates a digest without finalizing the MD5
+// operation.  Can be used to generate digests for the input seen thus far,
+// without affecting the digest generated for the entire input.
+BASE_EXPORT void MD5IntermediateFinal(MD5Digest* digest,
+                                      const MD5Context* context);
+
 // Converts a digest into human-readable hexadecimal.
 BASE_EXPORT std::string MD5DigestToBase16(const MD5Digest& digest);