Revert "Insert checks before deferred calls and accesses."

sdk/lib/_internal/lib/js_helper.dart

Index: sdk/lib/_internal/lib/js_helper.dart
diff --git a/sdk/lib/_internal/lib/js_helper.dart b/sdk/lib/_internal/lib/js_helper.dart
index 9147ae536e3aae27091536c0a31b24355b6255a4..73dd57ed8909f88a176d4dd459d3fffdae30a1af 100644
--- a/sdk/lib/_internal/lib/js_helper.dart
+++ b/sdk/lib/_internal/lib/js_helper.dart
@@ -2726,13 +2726,6 @@ checkMalformedType(value, message) {
   throw new TypeErrorImplementation.fromMessage(message);
 }
 
-@NoInline()
-void checkDeferredIsLoaded(String loadId, String uri) {
-  if (!_loadedLibraries.contains(loadId)) {
-    throw new DeferredNotLoadedError(uri);
-  }
-}
-
 /**
  * Special interface recognized by the compiler and implemented by DOM
  * objects that support integer indexing. This interface is not
@@ -2825,16 +2818,6 @@ class RuntimeError extends Error {
   String toString() => "RuntimeError: $message";
 }
 
-class DeferredNotLoadedError extends Error {
-  String libraryName;
-
-  DeferredNotLoadedError(this.libraryName);
-
-  String toString() {
-    return "Deferred library $libraryName was not loaded.";
-  }
-}
-
 abstract class RuntimeType {
   const RuntimeType();
 
@@ -3248,10 +3231,10 @@ LoadLibraryFunctionType _loadLibraryWrapper(String loadId) {
   return () => loadDeferredLibrary(loadId);
 }
 
-final Map<String, Future<Null>> _loadingLibraries = <String, Future<Null>>{};
-final Set<String> _loadedLibraries = new Set<String>();
+final Map<String, Future<Null>> _loadedLibraries = <String, Future<Null>>{};
+
+Future<bool> loadDeferredLibrary(String loadId, [String uri]) {
 
-Future<Null> loadDeferredLibrary(String loadId, [String uri]) {
   List<List<String>> hunkLists = JS('JSExtendableArray|Null',
       '\$.libraries_to_load[#]', loadId);
   if (hunkLists == null) return new Future.value(null);
@@ -3260,14 +3243,14 @@ Future<Null> loadDeferredLibrary(String loadId, [String uri]) {
     Iterable<Future<Null>> allLoads =
         hunkNames.map((hunkName) => _loadHunk(hunkName, uri));
     return Future.wait(allLoads).then((_) => null);
-  }).then((_) => _loadedLibraries.add(loadId));
+  });
 }
 
 Future<Null> _loadHunk(String hunkName, String uri) {
   // TODO(ahe): Validate libraryName.  Kasper points out that you want
   // to be able to experiment with the effect of toggling @DeferLoad,
   // so perhaps we should silently ignore "bad" library names.
-  Future<Null> future = _loadingLibraries[hunkName];
+  Future<Null> future = _loadedLibraries[hunkName];
   if (future != null) {
     return future.then((_) => null);
   }
@@ -3281,7 +3264,7 @@ Future<Null> _loadHunk(String hunkName, String uri) {
   if (Primitives.isJsshell || Primitives.isD8) {
     // TODO(ahe): Move this code to a JavaScript command helper script that is
     // not included in generated output.
-    return _loadingLibraries[hunkName] = new Future<Null>(() {
+    return _loadedLibraries[hunkName] = new Future<Null>(() {
       try {
         // Create a new function to avoid getting access to current function
         // context.
@@ -3293,7 +3276,7 @@ Future<Null> _loadHunk(String hunkName, String uri) {
     });
   } else if (isWorker()) {
     // We are in a web worker. Load the code with an XMLHttpRequest.
-    return _loadingLibraries[hunkName] = new Future<Null>(() {
+    return _loadedLibraries[hunkName] = new Future<Null>(() {
       Completer completer = new Completer<Null>();
       enterJsAsync();
       Future<Null> leavingFuture = completer.future.whenComplete(() {
@@ -3335,7 +3318,7 @@ Future<Null> _loadHunk(String hunkName, String uri) {
     });
   }
   // We are in a dom-context.
-  return _loadingLibraries[hunkName] = new Future<Null>(() {
+  return _loadedLibraries[hunkName] = new Future<Null>(() {
     Completer completer = new Completer<Null>();
     // Inject a script tag.
     var script = JS('', 'document.createElement("script")');