WebCrypto: Add interface for exportKey().

LayoutTests/crypto/resources/common.js

 function importTestKeys()
 {
     var keyFormat = "spki";
     var data = new Uint8Array([]);
-    var extractable = false;
+    var extractable = true;
     var keyUsages = ['encrypt', 'decrypt', 'sign', 'verify'];
 
     var hmacPromise = crypto.subtle.importKey(keyFormat, data, {name: 'hmac', hash: {name: 'sha-1'}}, extractable, keyUsages);
     var rsaSsaPromise = crypto.subtle.importKey(keyFormat, data, {name: 'RSASSA-PKCS1-v1_5', hash: {name: 'sha-1'}}, extractable, keyUsages);
     var aesCbcPromise = crypto.subtle.importKey(keyFormat, data, {name: 'AES-CBC'}, extractable, keyUsages);
-    var aesCbcJustDecrypt = crypto.subtle.importKey(keyFormat, data, {name: 'AES-CBC'}, extractable, ['decrypt']);
+    var aesCbcJustDecrypt = crypto.subtle.importKey(keyFormat, data, {name: 'AES-CBC'}, false, ['decrypt']);
 
     return Promise.every(hmacPromise, rsaSsaPromise, aesCbcPromise, aesCbcJustDecrypt).then(function(results) {
         return {
             hmacSha1: results[0],
             rsaSsaSha1: results[1],
             aesCbc: results[2],
             aesCbcJustDecrypt: results[3],
         };
     });
 }
@@ skipping 22 matching lines @@
         chars.push(str.charCodeAt(i));
     return new Uint8Array(chars);
 }
 
 function failAndFinishJSTest(error)
 {
     if (error)
        debug(error);
     finishJSTest();
 }