[webcrypto] Add the KeyAlgorithm interface.

LayoutTests/crypto/exportKey.html

Index: LayoutTests/crypto/exportKey.html
diff --git a/LayoutTests/crypto/exportKey.html b/LayoutTests/crypto/exportKey.html
index f5d6a932ea15b1295bbee99b0d820be08e9a051e..314ef16af2b22b433abab5bfc505f63908509f3b 100644
--- a/LayoutTests/crypto/exportKey.html
+++ b/LayoutTests/crypto/exportKey.html
@@ -28,7 +28,13 @@ addTask(importTestKeys().then(function(result) {
     shouldBe("keys.aesCbcJustDecrypt.extractable", "false")
     shouldRejectPromiseWithNull("crypto.subtle.exportKey('raw', keys.aesCbcJustDecrypt)");
 
-    // TODO(eroman): exportKey() is not implemented.
+    return crypto.subtle.exportKey('raw', keys.aesCbc);
+}).then(function(result) {
+    bytesShouldMatchHexString("Key bytes", "3136206279746573206f66206b657921", result);
+
+    return crypto.subtle.exportKey('spki', keys.rsaSsaSha1Public);
+}).then(function(result) {
+    bytesShouldMatchHexString("Key bytes", kPublicKeySpkiDerHex, result);
 }));
 
 completeTestWhenAllTasksDone();