MD5Update function uses StringPiece instead of raw buffer.

base/md5.h

Index: base/md5.h
diff --git a/base/md5.h b/base/md5.h
index a31732995668acb5ff5c363dafe125378326dfcf..a5af271c5e39a9c0f947b50692ae7a72cfb84c1e 100644
--- a/base/md5.h
+++ b/base/md5.h
@@ -9,6 +9,7 @@
 #include <string>
 
 #include "base/base_api.h"
+#include "base/string_piece.h"
 
 namespace base {
 
@@ -52,10 +53,10 @@ BASE_API void MD5Sum(const void* data, size_t length, MD5Digest* digest);
 // MD5Update().
 BASE_API void MD5Init(MD5Context* context);
 
-// For the given buffer of data, updates the given MD5 context with the sum of
-// the data. You can call this any number of times during the computation,
-// except that MD5Init() must have been called first.
-BASE_API void MD5Update(MD5Context* context, const void* data, size_t length);
+// For the given buffer of |data| as a StringPiece, updates the given MD5
+// context with the sum of the data. You can call this any number of times
+// during the computation, except that MD5Init() must have been called first.
+BASE_API void MD5Update(MD5Context* context, const StringPiece& data);
 
 // Finalizes the MD5 operation and fills the buffer with the digest.
 BASE_API void MD5Final(MD5Digest* digest, MD5Context* context);