Address a number of issues related to computation of currentScript and deferred loading.

dart/sdk/lib/_internal/compiler/implementation/js_backend/emitter.dart

Index: dart/sdk/lib/_internal/compiler/implementation/js_backend/emitter.dart
diff --git a/dart/sdk/lib/_internal/compiler/implementation/js_backend/emitter.dart b/dart/sdk/lib/_internal/compiler/implementation/js_backend/emitter.dart
index 06c9420cc5416e3f8b4b05464f532fab0c0754b0..07e1fce6985f48905e72fd4c6039e6ef0f9d518a 100644
--- a/dart/sdk/lib/_internal/compiler/implementation/js_backend/emitter.dart
+++ b/dart/sdk/lib/_internal/compiler/implementation/js_backend/emitter.dart
@@ -857,8 +857,6 @@ class CodeEmitterTask extends CompilerTask {
     return js.fun('oldIsolate', [
       js('var isolateProperties = oldIsolate.${namer.isolatePropertiesName}'),
 
-      js(r'isolateProperties.$currentScript = null'),
-
       js('var isolatePrototype = oldIsolate.prototype'),
       js('var str = "{\\n"'),
       js('str += "var properties = '
@@ -2962,8 +2960,7 @@ class CodeEmitterTask extends CompilerTask {
     scripts[i].addEventListener('load', onLoad, false);
   }
 })(function(currentScript) {
-  ${namer.isolateName}.${namer.isolatePropertiesName}.\$currentScript =
-      currentScript;
+  init.currentScript = currentScript;
 
   if (typeof console !== 'undefined' && typeof document !== 'undefined' &&
       document.readyState == "loading") {