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

crypto/encryptor_mac.cc

Index: crypto/encryptor_mac.cc
diff --git a/crypto/encryptor_mac.cc b/crypto/encryptor_mac.cc
index 6be373a5d92028052b1de94d5f1d85739b54ffcf..972fc0432403a0ba7379f04d1de2957af6b7aa70 100644
--- a/crypto/encryptor_mac.cc
+++ b/crypto/encryptor_mac.cc
@@ -23,8 +23,10 @@ Encryptor::~Encryptor() {
 bool Encryptor::Init(SymmetricKey* key,
                      Mode mode,
                      const base::StringPiece& iv) {
-  DCHECK(key);
-  DCHECK_EQ(CBC, mode) << "Unsupported mode of operation";
+  DCHECK_EQ(CBC, mode);
+  if (!key)
+    return false;
+
   CSSM_DATA raw_key = key->cssm_data();
   if (raw_key.Length != kCCKeySizeAES128 &&
       raw_key.Length != kCCKeySizeAES192 &&
@@ -42,15 +44,17 @@ bool Encryptor::Init(SymmetricKey* key,
 bool Encryptor::Crypt(int /*CCOperation*/ op,
                       const base::StringPiece& input,
                       std::string* output) {
-  DCHECK(key_);
+  if (!key_)
+    return false;
+
   CSSM_DATA raw_key = key_->cssm_data();
   // CommonCryptor.h: "A general rule for the size of the output buffer which
   // must be provided by the caller is that for block ciphers, the output
   // length is never larger than the input length plus the block size."
-
   size_t output_size = input.size() + iv_.size();
-  CHECK_GT(output_size, 0u);
-  CHECK_GT(output_size + 1, input.size());
+  if (output_size == 0 || output_size + 1 < input.size())
+    return false;
+
   CCCryptorStatus err = CCCrypt(op,
                                 kCCAlgorithmAES128,
                                 kCCOptionPKCS7Padding,
@@ -61,7 +65,6 @@ bool Encryptor::Crypt(int /*CCOperation*/ op,
                                 output_size,
                                 &output_size);
   if (err) {
-    output->clear();
     LOG(ERROR) << "CCCrypt returned " << err;
     return false;
   }
@@ -71,13 +74,15 @@ bool Encryptor::Crypt(int /*CCOperation*/ op,
 
 bool Encryptor::Encrypt(const base::StringPiece& plaintext,
                         std::string* ciphertext) {
-  CHECK(!plaintext.empty() || (mode_ == CBC));
+  if (plaintext.empty() && mode_ != CBC)
+    return false;
   return Crypt(kCCEncrypt, plaintext, ciphertext);
 }
 
 bool Encryptor::Decrypt(const base::StringPiece& ciphertext,
                         std::string* plaintext) {
-  CHECK(!ciphertext.empty());
+  if (ciphertext.empty())
+    return false;
   return Crypt(kCCDecrypt, ciphertext, plaintext);
 }