Support web workers in dart2js.

sdk/lib/_internal/compiler/implementation/lib/js_helper.dart

Index: sdk/lib/_internal/compiler/implementation/lib/js_helper.dart
===================================================================
--- sdk/lib/_internal/compiler/implementation/lib/js_helper.dart	(revision 16024)
+++ sdk/lib/_internal/compiler/implementation/lib/js_helper.dart	(working copy)
@@ -1117,13 +1117,16 @@
   if (closure == null) return null;
   var function = JS('var', r'#.$identity', closure);
   if (JS('bool', r'!!#', function)) return function;
+  // Fetch the current isolate in a local variable to prevent the

[kasperl, 2012/12/13 08:45:12]

Extend comment to mention that the current isolate may have changed so if we
read it from within the JS closure it leads to the wrong thing.

[ngeoffray, 2012/12/13 11:56:15]

Done.

+  // compiler from inlining its use in the following JS expression.
+  var currentIsolate = JS_CURRENT_ISOLATE();
 
   function = JS("var", r"""function() {
     return #(#, #, #, arguments[0], arguments[1]);
   }""",
   DART_CLOSURE_TO_JS(invokeClosure),
   closure,
-  JS_CURRENT_ISOLATE(),
+  currentIsolate,
   arity);
 
   JS('void', r'#.$identity = #', closure, function);