Use shouldBecomeEqual in asynchronous spellchecking tests.

LayoutTests/editing/spelling/move-cursor-to-misspelled-word.html

Index: LayoutTests/editing/spelling/move-cursor-to-misspelled-word.html
diff --git a/LayoutTests/editing/spelling/move-cursor-to-misspelled-word.html b/LayoutTests/editing/spelling/move-cursor-to-misspelled-word.html
index bb0c3a03dac99a60de71cd503579451ef0293c17..25c11937ca28266a2319f9a1ac5ea98dfed5f47c 100644
--- a/LayoutTests/editing/spelling/move-cursor-to-misspelled-word.html
+++ b/LayoutTests/editing/spelling/move-cursor-to-misspelled-word.html
@@ -10,6 +10,8 @@ description('Test if Chrome WebKit does not remove a misspelled marker when movi
             'To test manually, type a misspelled word "zz " and type a left-arrow key to move the cursor on it.' +
             'This test succeeds when "zz" is marked as misspelled.');
 
+jsTestIsAsync = true;
+
 internals.settings.setAsynchronousSpellCheckingEnabled(true);
 var node = document.getElementById('src');
 node.focus();
@@ -17,7 +19,7 @@ document.execCommand("InsertText", false, 'z');
 document.execCommand("InsertText", false, 'z');
 document.execCommand("InsertText", false, ' ');
 window.getSelection().modify('move', 'backward', 'character');
-shouldBeTrue('internals.hasSpellingMarker(document, 0, 2)');
+shouldBecomeEqual('internals.hasSpellingMarker(document, 0, 2)', 'true', finishJSTest);
 </script>
 <script src="../../fast/js/resources/js-test-post.js"></script>
 </body>