WebCrypto: Add interfaces for importKey().

Source/modules/crypto/Key.idl

Index: Source/modules/crypto/Key.idl
diff --git a/Source/modules/crypto/Key.idl b/Source/modules/crypto/Key.idl
index ef447f034d4714f17ca97877852332df2ca24752..6124a2f57462bfb7150ddcf317d3bb7b8a9779ed 100644
--- a/Source/modules/crypto/Key.idl
+++ b/Source/modules/crypto/Key.idl
@@ -28,27 +28,11 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
-enum KeyType {
-    "secret",
-    "public",
-    "private"
-};
-
-enum KeyUsage {
-    "encrypt",
-    "decrypt",
-    "sign",
-    "verify",
-    "deriveKey",
-    "wrapKey",
-    "unwrapKey"
-};
-
 [
     NoInterfaceObject,
 ] interface Key {
-    readonly attribute KeyType type;
+    readonly attribute DOMString type;
     readonly attribute boolean extractable;
     readonly attribute Algorithm algorithm;
-    readonly attribute KeyUsage[] usages;
+    readonly attribute DOMString[] usages;
 };