Cleanup the isolate library to pave the way for web worker support.

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

Index: sdk/lib/_internal/compiler/implementation/lib/foreign_helper.dart
===================================================================
--- sdk/lib/_internal/compiler/implementation/lib/foreign_helper.dart	(revision 16903)
+++ sdk/lib/_internal/compiler/implementation/lib/foreign_helper.dart	(working copy)
@@ -91,7 +91,7 @@
     [var arg0, var arg1, var arg2]) {}
 
 /**
- * Invoke a method without the compiler trying to intercept it.
+ * Invokes a method without the compiler trying to intercept it.
  */
 dynamic UNINTERCEPTED(var expression) {}
 
@@ -106,11 +106,21 @@
 dynamic JS_CURRENT_ISOLATE() {}
 
 /**
- * Invoke [function] in the context of [isolate].
+ * Invokes [function] in the context of [isolate].
  */
 dynamic JS_CALL_IN_ISOLATE(var isolate, Function function) {}
 
 /**
- * Convers the Dart closure [function] into a JavaScript closure.
+ * Converts the Dart closure [function] into a JavaScript closure.
  */
 dynamic DART_CLOSURE_TO_JS(Function function) {}
+
+/**
+ * Sets the current isolate to [isolate].
+ */
+void JS_SET_CURRENT_ISOLATE(var isolate) {}
+
+/**
+ * Creates an isolate and returns it.
+ */
+dynamic JS_CREATE_ISOLATE() {}