Make string_util::WriteInto() DCHECK() that the supplied |length_with_null| > 1, meaning that the...

crypto/encryptor.h

Index: crypto/encryptor.h
===================================================================
--- crypto/encryptor.h	(revision 111826)
+++ crypto/encryptor.h	(working copy)
@@ -61,13 +61,15 @@
   // Initializes the encryptor using |key| and |iv|. Returns false if either the
   // key or the initialization vector cannot be used.
   //
-  // When |mode| is CTR then |iv| should be empty.
+  // If |mode| is CBC, |iv| must not be empty; if it is CTR, then |iv| must be
+  // empty.
   bool Init(SymmetricKey* key, Mode mode, const base::StringPiece& iv);
 
-  // Encrypts |plaintext| into |ciphertext|.
+  // Encrypts |plaintext| into |ciphertext|.  |plaintext| may only be empty if
+  // the mode is CBC.
   bool Encrypt(const base::StringPiece& plaintext, std::string* ciphertext);
 
-  // Decrypts |ciphertext| into |plaintext|.
+  // Decrypts |ciphertext| into |plaintext|.  |ciphertext| must not be empty.
   bool Decrypt(const base::StringPiece& ciphertext, std::string* plaintext);
 
   // Sets the counter value when in CTR mode. Currently only 128-bits