Fix one more failing test due to assert_throws() w/ a null exception

Bug: 711529
Change-Id: Id64a48214d682f5feba6f6a5f301b394e4a6ce42
Reviewed-on: https://chromium-review.googlesource.com/806274Reviewed-by: Mike West <mkwst@chromium.org>
Commit-Queue: Peter Beverloo <peter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#522439}

third_party/WebKit/LayoutTests/TestExpectations

@@ -1907,7 +1907,6 @@ crbug.com/704259 external/wpt/content-security-policy/reporting/reporting-api-se
 crbug.com/711529 http/tests/origin_trials/sample-api-workers.html [ Crash Timeout ]
 crbug.com/711529 http/tests/permissions/test-api-surface.html [ Timeout ]
 crbug.com/711529 http/tests/permissions/test-query.html [ Timeout ]
-crbug.com/711529 http/tests/security/cross-origin-createImageBitmap-structured-clone.html [ Timeout ]
 crbug.com/711529 http/tests/workers/shared-worker-performance-timeline.html [ Timeout ]
 
 # Expected failures during incremental implementation of mojo notification.

third_party/WebKit/LayoutTests/http/tests/security/cross-origin-createImageBitmap-structured-clone.html

@@ -39,7 +39,7 @@ async_test(function(t) {
         canvas.height = 10;
         var context = canvas.getContext("2d");
         context.drawImage(imageBitmap, 0, 0, 10, 10);
-        assert_throws(null, function () { context.getImageData(0, 0, 10, 10); }, 'ImageBitmap should be tainted');
+        assert_throws('SecurityError', function () { context.getImageData(0, 0, 10, 10); }, 'ImageBitmap should be tainted');
     }
 }, 'Transfer and structured-clone an ImageBitmap should preserve the originClean flag.');
 </script>