[webcrypto] Implement AES-CTR using BoringSSL.

BUG=399084

Review URL: https://codereview.chromium.org/491763002

Cr-Commit-Position: refs/heads/master@{#292053}
diff --git a/content/child/webcrypto/algorithm_registry.cc b/content/child/webcrypto/algorithm_registry.cc
index eda5ba2..af1b4bd 100644
--- a/content/child/webcrypto/algorithm_registry.cc
+++ b/content/child/webcrypto/algorithm_registry.cc
@@ -21,6 +21,7 @@
       : sha_(CreatePlatformShaImplementation()),
         aes_gcm_(CreatePlatformAesGcmImplementation()),
         aes_cbc_(CreatePlatformAesCbcImplementation()),
+        aes_ctr_(CreatePlatformAesCtrImplementation()),
         aes_kw_(CreatePlatformAesKwImplementation()),
         hmac_(CreatePlatformHmacImplementation()),
         rsa_ssa_(CreatePlatformRsaSsaImplementation()),
@@ -40,6 +41,8 @@
         return aes_gcm_.get();
       case blink::WebCryptoAlgorithmIdAesCbc:
         return aes_cbc_.get();
+      case blink::WebCryptoAlgorithmIdAesCtr:
+        return aes_ctr_.get();
       case blink::WebCryptoAlgorithmIdAesKw:
         return aes_kw_.get();
       case blink::WebCryptoAlgorithmIdHmac:
@@ -57,6 +60,7 @@
   scoped_ptr<AlgorithmImplementation> sha_;
   scoped_ptr<AlgorithmImplementation> aes_gcm_;
   scoped_ptr<AlgorithmImplementation> aes_cbc_;
+  scoped_ptr<AlgorithmImplementation> aes_ctr_;
   scoped_ptr<AlgorithmImplementation> aes_kw_;
   scoped_ptr<AlgorithmImplementation> hmac_;
   scoped_ptr<AlgorithmImplementation> rsa_ssa_;