Rewrite the 'window.onerror' tests.

LayoutTests/fast/events/resources/onerror-test.js

+if (window.testRunner)

[do-not-use, 2013/07/23 14:46:09]

Would becomes optional if we used js-test-pre.js

+    testRunner.dumpAsText();
+
+var output;
+
+function log(message) {

[do-not-use, 2013/07/23 14:46:09]

Any reason we are not using js-test-pre.js? We could use
testPassed()/testFailed()/debug() instead of rewriting a log() function.

[Mike West, 2013/07/23 14:51:54]

I thought about it, and decided that the advantage was slim since we're
generally dumping values directly into the expectations file, and only rarely
want to make assertions that valueA is X.

But since you've mentioned it too, it's probably the right thing to do. I'll
take another pass tomorrow.

+    if (!output) {
+        output = document.createElement('pre')
+        document.body.appendChild(output);
+    }
+
+    output.appendChild(document.createTextNode(message + "\n"));
+}
+
+function stripURL(url) {
+    return url ? url.match( /[^\/]+\/?$/ )[0] : url;
+}
+
+function throwException(message) {
+    throw new Error(message ? message : "An exception");
+}
+
+function DumpOnErrorArgumentValuesAndReturn(returnValue, callback) {
+    window.onerror = function (message, url, line, column) {
+        log("window.onerror: \"" + message + "\" at " + stripURL(url) + " (" + line + ", " + column + ")");
+        if (callback)
+            callback();
+        if (returnValue)
+            log("- Returning 'true': the error should not be reported in the console as an unhandled exception.");
+        else
+            log("- Returning 'false': the error should be reported in the console as an unhandled exception.");
+        return returnValue;
+    };
+}
+
+function DumpErrorEventAndAllowDefault(callback) {
+    window.addEventListener('error', function (e) {
+        DumpErrorEvent(e)
+        log("- Not calling e.preventDefault(): the error should be reported in the console as an unhandled exception.");
+        if (callback)
+            callback();
+    });
+}
+
+function DumpErrorEventAndPreventDefault(callback) {
+    window.addEventListener('error', function (e) {
+        DumpErrorEvent(e);
+        log("- Calling e.preventDefault(): the error should not be reported in the console as an unhandled exception.");
+        e.preventDefault();
+        if (callback)
+            callback();
+    });
+}
+
+function DumpErrorEvent(e) {
+    log("Handling '" + e.type + "' event (phase " + e.eventPhase + "): \"" + e.message + "\" at " + stripURL(e.filename) + ":" + e.lineno);
+
+    log("PASS: event passed to the listener is the same as 'window.event': " + (window.event === e));
+    log("PASS: 'currentTarget' is the global object: " + (e.currentTarget === window));
+}