Fix typo in headers comment.

pkg/compiler/lib/src/js_emitter/headers.dart

Index: pkg/compiler/lib/src/js_emitter/headers.dart
diff --git a/pkg/compiler/lib/src/js_emitter/headers.dart b/pkg/compiler/lib/src/js_emitter/headers.dart
index 2bdb761002da4fd4bb26ddf19d6285f1394a1d57..905cb04f048f4aae1256af388d55e2dd22abd492 100644
--- a/pkg/compiler/lib/src/js_emitter/headers.dart
+++ b/pkg/compiler/lib/src/js_emitter/headers.dart
@@ -28,7 +28,7 @@ const String HOOKS_API_USAGE = """
 //    [args] is passed to [dartMainRunner].
 //
 // dartDeferredLibraryLoader(uri, successCallback, errorCallback):
-//    if this function is defined, it will be called when a deferered library
+//    if this function is defined, it will be called when a deferred library
 //    is loaded. It should load and eval the javascript of `uri`, and call
 //    successCallback. If it fails to do so, it should call errorCallback with
 //    an error.