Add WARN_UNUSED_RESULT to crypto/hmac.h

crypto/hmac_mac.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "crypto/hmac.h"
 
 #include <CommonCrypto/CommonHMAC.h>
 
 #include "base/logging.h"
 
@@ skipping 24 matching lines @@
 HMAC::~HMAC() {
   // Zero out key copy.
   plat_->key_.assign(plat_->key_.length(), std::string::value_type());
   plat_->key_.clear();
   plat_->key_.reserve(0);
 }
 
 bool HMAC::Sign(const base::StringPiece& data,
                 unsigned char* digest,
                 int digest_length) const {
+  if (plat_->key_.empty()) {
+    // Init has not been called or has failed.
+    NOTREACHED();
+    return false;
+  }
+
   CCHmacAlgorithm algorithm;
   int algorithm_digest_length;
   switch (hash_alg_) {
     case SHA1:
       algorithm = kCCHmacAlgSHA1;
       algorithm_digest_length = CC_SHA1_DIGEST_LENGTH;
       break;
     case SHA256:
       algorithm = kCCHmacAlgSHA256;
       algorithm_digest_length = CC_SHA256_DIGEST_LENGTH;
       break;
     default:
       NOTREACHED();
       return false;
   }
 
   if (digest_length < algorithm_digest_length) {
     NOTREACHED();
     return false;
   }
 
   CCHmac(algorithm,
          plat_->key_.data(), plat_->key_.length(), data.data(), data.length(),
          digest);
 
   return true;
 }
 
 }  // namespace crypto