Onerror return value handling in workers fixed as per HTML5 spec.

LayoutTests/fast/workers/resources/worker-error-handler-worker.js

Index: LayoutTests/fast/workers/resources/worker-error-handler-worker.js
diff --git a/LayoutTests/fast/workers/resources/worker-error-handler-worker.js b/LayoutTests/fast/workers/resources/worker-error-handler-worker.js
new file mode 100644
index 0000000000000000000000000000000000000000..45af377b9f6a737ee8206a97ee0803f4243baae2
--- /dev/null
+++ b/LayoutTests/fast/workers/resources/worker-error-handler-worker.js
@@ -0,0 +1,10 @@
+self.onerror = function(e){
+    postMessage("workerGlobalScopeErrorHandlerInvoked");
+    // We have nor cancelled this error event, hence it should
+    // be propagated to the worker.onerror error handler.
+    return false;
+}
+
+self.onmessage= function(e){
+    foo.bar = 0;
+}