Deal with deferred loading in the VM mirrors.

sdk/lib/mirrors/mirrors.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 // For the purposes of the mirrors library, we adopt a naming
 // convention with respect to getters and setters.  Specifically, for
 // some variable or field...
 //
 //   var myField;
 //
@@ skipping 37 matching lines @@
  *
  * ## Status: Unstable
  *
  * The dart:mirrors library is unstable and its API might change slightly as a
  * result of user feedback. This library is platform dependent and therefore it
  * has implementations for both dart2js and the Dart VM. Both are under
  * development and may not support all operations yet.
  */
 library dart.mirrors;
 
+import 'dart:async' show Future;
+
 /**
  * A [MirrorSystem] is the main interface used to reflect on a set of
  * associated libraries.
  *
  * At runtime each running isolate has a distinct [MirrorSystem].
  *
  * It is also possible to have a [MirrorSystem] which represents a set
  * of libraries which are not running -- perhaps at compile-time.  In
  * this case, all available reflective functionality would be
  * supported, but runtime functionality (such as invoking a function
@@ skipping 537 matching lines @@
   bool get isExport;
 
   /// Returns true iff this dependency is a deferred import. Otherwise returns
   /// false.
   bool get isDeferred;
 
   /// Returns the library mirror of the library that imports or exports the
   /// [targetLibrary].
   LibraryMirror get sourceLibrary;
 
-  /// Returns the library mirror of the library that is imported or exported.
+  /// Returns the library mirror of the library that is imported or exported,
+  /// or null if the library is not loaded.
   LibraryMirror get targetLibrary;
 
   /// Returns the prefix if this is a prefixed import and `null` otherwise.
   Symbol get prefix;
 
   /// Returns the list of show/hide combinators on the import/export
   /// declaration.
   List<CombinatorMirror> get combinators;
 
   /// Returns the source location for this import/export declaration.
   SourceLocation get location;
 
   List<InstanceMirror> get metadata;
+
+  /// Returns a future that completes with a library mirror on the library being
+  /// imported or exported when it is loaded, and initiates a load of that
+  /// library if it is not loaded.
+  Future<LibraryMirror> loadLibrary();
 }
 
 /// A mirror on a show/hide combinator declared on a library dependency.
 abstract class CombinatorMirror implements Mirror {
   /// The list of identifiers on the combinator.
   List<Symbol> get identifiers;
 
   /// Is `true` if this is a 'show' combinator.
   bool get isShow;
 
@@ skipping 622 matching lines @@
    *
    * When used as metadata on an import of "dart:mirrors", this metadata does
    * not apply to the library in which the annotation is used, but instead
    * applies to the other libraries (all libraries if "*" is used).
    */
   final override;
 
   const MirrorsUsed(
       {this.symbols, this.targets, this.metaTargets, this.override});
 }