Support for a dart2js `dartDeferredLoader` hook.

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

Index: sdk/lib/_internal/compiler/js_lib/js_helper.dart
diff --git a/sdk/lib/_internal/compiler/js_lib/js_helper.dart b/sdk/lib/_internal/compiler/js_lib/js_helper.dart
index 1b33108bd3b0a86bad1e98c4c6d815962d61dfd8..49f53ed6c08d37b3bfc8d554261455cfba3c253e 100644
--- a/sdk/lib/_internal/compiler/js_lib/js_helper.dart
+++ b/sdk/lib/_internal/compiler/js_lib/js_helper.dart
@@ -3451,9 +3451,6 @@ Future<Null> loadDeferredLibrary(String loadId) {
 }
 
 Future<Null> _loadHunk(String hunkName) {
-  // 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];
   if (future != null) {
     return future.then((_) => null);
@@ -3464,87 +3461,74 @@ Future<Null> _loadHunk(String hunkName) {
   int index = uri.lastIndexOf('/');
   uri = '${uri.substring(0, index + 1)}$hunkName';
 
-  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>(() {
+  var deferredLibraryLoader = JS('', 'self.dartDeferredLibraryLoader');
+  Completer<Null> completer = new Completer<Null>();
+
+  void success() {
+    completer.complete(null);
+  }
+
+  void failure([error, StackTrace stackTrace]) {
+    _loadingLibraries[hunkName] = null;
+    completer.completeError(
+        new DeferredLoadException("Loading $uri failed: $error"),
+        stackTrace);
+  }
+
+  var jsSuccess = convertDartClosureToJS(success, 0);
+  var jsFailure = convertDartClosureToJS((error) {
+    failure(unwrapException(error), getTraceFromException(error));
+  }, 1);
+
+  if (JS('bool', 'typeof # === "function"', deferredLibraryLoader)) {
+    try {
+      JS('void', '#(#, #, #)', deferredLibraryLoader, uri,
+          jsSuccess, jsFailure);
+    } catch (error, stackTrace) {
+      failure(error, stackTrace);
+    }
+  } else if (isWorker()) {
+    // We are in a web worker. Load the code with an XMLHttpRequest.
+    enterJsAsync();
+    Future<Null> leavingFuture = completer.future.whenComplete(() {
+      leaveJsAsync();
+    });
+
+    int index = uri.lastIndexOf('/');
+    uri = '${uri.substring(0, index + 1)}$hunkName';
+    var xhr = JS('dynamic', 'new XMLHttpRequest()');
+    JS('void', '#.open("GET", #)', xhr, uri);
+    JS('void', '#.addEventListener("load", #, false)',
+       xhr, convertDartClosureToJS((event) {
+      if (JS('int', '#.status', xhr) != 200) {
+        failure("");
+      }
+      String code = JS('String', '#.responseText', xhr);
       try {
         // Create a new function to avoid getting access to current function
         // context.
-        JS('void', '(new Function(#))()', 'load("$uri")');
+        JS('void', '(new Function(#))()', code);
+        success();
       } catch (error, stackTrace) {
-        _loadingLibraries[hunkName] = null;
-        throw new DeferredLoadException("Loading $uri failed.");
+        failure(error, stackTrace);
       }
-      return null;
-    });
-  } else if (isWorker()) {
-    // We are in a web worker. Load the code with an XMLHttpRequest.
-    return _loadingLibraries[hunkName] = new Future<Null>(() {
-      Completer completer = new Completer<Null>();
-      enterJsAsync();
-      Future<Null> leavingFuture = completer.future.whenComplete(() {
-        leaveJsAsync();
-      });
+    }, 1));
 
-      int index = uri.lastIndexOf('/');
-      uri = '${uri.substring(0, index + 1)}$hunkName';
-      var xhr = JS('dynamic', 'new XMLHttpRequest()');
-      JS('void', '#.open("GET", #)', xhr, uri);
-      JS('void', '#.addEventListener("load", #, false)',
-         xhr, convertDartClosureToJS((event) {
-        if (JS('int', '#.status', xhr) != 200) {
-          _loadingLibraries[hunkName] = null;
-          completer.completeError(
-              new DeferredLoadException("Loading $uri failed."));
-          return;
-        }
-        String code = JS('String', '#.responseText', xhr);
-        try {
-          // Create a new function to avoid getting access to current function
-          // context.
-          JS('void', '(new Function(#))()', code);
-        } catch (error, stackTrace) {
-          _loadingLibraries[hunkName] = null;
-          completer.completeError(
-            new DeferredLoadException("Evaluating $uri failed."));
-          return;
-        }
-        completer.complete(null);
-      }, 1));
-
-      var fail = convertDartClosureToJS((event) {
-        _loadingLibraries[hunkName] = null;
-        new DeferredLoadException("Loading $uri failed.");
-      }, 1);
-      JS('void', '#.addEventListener("error", #, false)', xhr, fail);
-      JS('void', '#.addEventListener("abort", #, false)', xhr, fail);
-
-      JS('void', '#.send()', xhr);
-      return leavingFuture;
-    });
-  }
-  // We are in a dom-context.
-  return _loadingLibraries[hunkName] = new Future<Null>(() {
-    Completer completer = new Completer<Null>();
+    JS('void', '#.addEventListener("error", #, false)', xhr, failure);
+    JS('void', '#.addEventListener("abort", #, false)', xhr, failure);
+    JS('void', '#.send()', xhr);
+  } else {
+    // We are in a dom-context.
     // Inject a script tag.
     var script = JS('', 'document.createElement("script")');
     JS('', '#.type = "text/javascript"', script);
     JS('', '#.src = #', script, uri);
-    JS('', '#.addEventListener("load", #, false)',
-       script, convertDartClosureToJS((event) {
-      completer.complete(null);
-    }, 1));
-    JS('', '#.addEventListener("error", #, false)',
-       script, convertDartClosureToJS((event) {
-      _loadingLibraries[hunkName] = null;
-      completer.completeError(
-          new DeferredLoadException("Loading $uri failed."));
-    }, 1));
+    JS('', '#.addEventListener("load", #, false)', script, jsSuccess);
+    JS('', '#.addEventListener("error", #, false)', script, jsFailure);
     JS('', 'document.body.appendChild(#)', script);
-
-    return completer.future;
-  });
+  }
+  _loadingLibraries[hunkName] = completer.future;
+  return completer.future;
 }
 
 class MainError extends Error implements NoSuchMethodError {