Improve the mirror support for deferred loading.

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

Index: sdk/lib/_internal/compiler/implementation/compiler.dart
diff --git a/sdk/lib/_internal/compiler/implementation/compiler.dart b/sdk/lib/_internal/compiler/implementation/compiler.dart
index c756277a8f02eea7e5c69bfaf008adcc7d05496b..b5e2a184f4fc480c70e3c76c851fe4d7325dc762 100644
--- a/sdk/lib/_internal/compiler/implementation/compiler.dart
+++ b/sdk/lib/_internal/compiler/implementation/compiler.dart
@@ -352,6 +352,14 @@ abstract class Compiler implements DiagnosticListener {
    */
   final TreeElements globalDependencies = new TreeElementMapping(null);
 
+  /**
+   * Dependencies that are only included due to mirrors.
+   *
+   * We should get rid of this and ensure that all dependencies are
+   * associated with a particular element.
+   */
+  final TreeElements mirrorDependencies = new TreeElementMapping(null);
+
   final bool enableMinification;
   final bool enableTypeAssertions;
   final bool enableUserAssertions;