Unify the error checking of crypto::Encryptor and add WARN_UNUSED_RESULT to prevent misuse.

crypto/encryptor.h

Index: crypto/encryptor.h
diff --git a/crypto/encryptor.h b/crypto/encryptor.h
index 6b236199e75dcbea6532c881388315f7bfae6580..5e919ca5e7e3c1ce650e0e689d1ae4809f8c2082 100644
--- a/crypto/encryptor.h
+++ b/crypto/encryptor.h
@@ -9,6 +9,7 @@
 #include <string>
 
 #include "base/basictypes.h"
+#include "base/compiler_specific.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/string_piece.h"
 #include "build/build_config.h"
@@ -39,7 +40,7 @@ class CRYPTO_EXPORT Encryptor {
     ~Counter();
 
     // Increment the counter value.
-    bool Increment();
+    bool Increment() WARN_UNUSED_RESULT;
 
     // Write the content of the counter to |buf|. |buf| should have enough
     // space for |GetLengthInBytes()|.
@@ -63,20 +64,24 @@ class CRYPTO_EXPORT Encryptor {
   //
   // 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);
+  bool Init(SymmetricKey* key,
+            Mode mode,
+            const base::StringPiece& iv) WARN_UNUSED_RESULT;
 
   // Encrypts |plaintext| into |ciphertext|.  |plaintext| may only be empty if
   // the mode is CBC.
-  bool Encrypt(const base::StringPiece& plaintext, std::string* ciphertext);
+  bool Encrypt(const base::StringPiece& plaintext,
+               std::string* ciphertext) WARN_UNUSED_RESULT;
 
   // Decrypts |ciphertext| into |plaintext|.  |ciphertext| must not be empty.
-  bool Decrypt(const base::StringPiece& ciphertext, std::string* plaintext);
+  bool Decrypt(const base::StringPiece& ciphertext,
+               std::string* plaintext) WARN_UNUSED_RESULT;
 
   // Sets the counter value when in CTR mode. Currently only 128-bits
   // counter value is supported.
   //
   // Returns true only if update was successful.
-  bool SetCounter(const base::StringPiece& counter);
+  bool SetCounter(const base::StringPiece& counter) WARN_UNUSED_RESULT;
 
   // TODO(albertb): Support streaming encryption.