Rewrite the 'window.onerror' tests.

LayoutTests/fast/events/window-onerror-12-expected.txt

Index: LayoutTests/fast/events/window-onerror-12-expected.txt
diff --git a/LayoutTests/fast/events/window-onerror-12-expected.txt b/LayoutTests/fast/events/window-onerror-12-expected.txt
new file mode 100644
index 0000000000000000000000000000000000000000..15fb572ee4bda97b72f481a38693ffb4b04a6a6f
--- /dev/null
+++ b/LayoutTests/fast/events/window-onerror-12-expected.txt
@@ -0,0 +1,15 @@
+CONSOLE MESSAGE: line 14: 1
+CONSOLE MESSAGE: line 14: 2
+CONSOLE MESSAGE: line 14: 3
+window.onerror: "Uncaught TypeError: Cannot call method 'mu' of null" at window-onerror-12.html (9, 74)
+- Returning 'true': the error should not be reported in the console as an unhandled exception.
+window.onerror: "Uncaught TypeError: Cannot call method 'mu' of null" at window-onerror-12.html (32, 74)
+- Returning 'true': the error should not be reported in the console as an unhandled exception.
+window.onerror: "Uncaught TypeError: Cannot call method 'mu' of null" at window-onerror-12.html (32, 74)
+- Returning 'true': the error should not be reported in the console as an unhandled exception.
+PASS successfullyParsed is true
+
+TEST COMPLETE
+This test should trigger 'window.onerror' for the exception in the attribute handler, regardless of how it's set.
+
+Button.  Button 2 Button 3