[webcrypto] Add parameter parsing for AES-GCM.

LayoutTests/crypto/resources/common.js

 function importTestKeys()
 {
     var keyFormat = "raw";
     var data = asciiToUint8Array("16 bytes of key!");
     var extractable = true;
     var keyUsages = ['wrapKey', 'unwrapKey', 'encrypt', 'decrypt', 'sign', 'verify'];
 
     var hmacPromise = crypto.subtle.importKey(keyFormat, data, {name: 'hmac', 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'}, false, ['decrypt']);
     // FIXME: use AES-CTR key type once it's implemented
     var aesCtrPromise = crypto.subtle.importKey(keyFormat, data, {name: 'AES-CBC'}, extractable, keyUsages);
+    var aesGcmPromise = crypto.subtle.importKey(keyFormat, data, {name: 'AES-GCM'}, extractable, keyUsages);
 
-    return Promise.all([hmacPromise, aesCbcPromise, aesCbcJustDecrypt, aesCtrPromise]).then(function(results) {
+    return Promise.all([hmacPromise, aesCbcPromise, aesCbcJustDecrypt, aesCtrPromise, aesGcmPromise]).then(function(results) {
         return {
             hmacSha1: results[0],
             aesCbc: results[1],
             aesCbcJustDecrypt: results[2],
             aesCtr: results[3],
+            aesGcm: results[4],
         };
     });
 }
 
 // Verifies that the given "bytes" holds the same value as "expectedHexString".
 // "bytes" can be anything recognized by "bytesToHexString()".
 function bytesShouldMatchHexString(testDescription, expectedHexString, bytes)
 {
     expectedHexString = "[" + expectedHexString.toLowerCase() + "]";
     var actualHexString = "[" + bytesToHexString(bytes) + "]";
@@ skipping 109 matching lines @@
         debug("PASS: '" + code + "' accepted with " + result);
     }
 
     function rejectCallback(result)
     {
         debug("FAIL: '" + code + "' rejected with " + result);
     }
 
     addTask(promise.then(acceptCallback, rejectCallback));
 }