[webcrypto] Don't throw any extra WebIDL exceptions from WebCrypto methods.

LayoutTests/crypto/exportKey-badParameters.html

Index: LayoutTests/crypto/exportKey-badParameters.html
diff --git a/LayoutTests/crypto/exportKey-badParameters.html b/LayoutTests/crypto/exportKey-badParameters.html
index 638d8b47b5768c74ed29cbbcb8805ff839957756..61244af2f04e1d586ba1e93a3c36deef573dba24 100644
--- a/LayoutTests/crypto/exportKey-badParameters.html
+++ b/LayoutTests/crypto/exportKey-badParameters.html
@@ -13,10 +13,6 @@ description("Tests exportKey() given bad inputs.");
 
 jsTestIsAsync = true;
 
-// Not keys
-shouldThrow("crypto.subtle.exportKey('raw', null)");
-shouldThrow("crypto.subtle.exportKey('raw', 3)");
-
 function importAesKey()
 {
     var keyData = new Uint8Array(16);
@@ -27,7 +23,21 @@ function importAesKey()
     return crypto.subtle.importKey('raw', keyData, algorithm, extractable, usages);
 }
 
-importAesKey().then(function(result) {
+Promise.resolve(null).then(function(result) {
+    // null is not a valid Key.
+    return crypto.subtle.exportKey('raw', null);
+}).then(failAndFinishJSTest, function(result) {
+    error = result;
+    shouldBeNull("error");
+
+    // 3 is not a valid Key.
+    return crypto.subtle.exportKey('raw', 3);
+}).then(failAndFinishJSTest, function(result) {
+    error = result;
+    shouldBeNull("error");
+
+    return importAesKey();
+}).then(function(result) {
     key = result;
 
     // Invalid export format