Reapply "Access to imports in the VM's runtime mirrors. Extend test coverage of the source mirrors."

sdk/lib/_internal/lib/js_mirrors.dart

Index: sdk/lib/_internal/lib/js_mirrors.dart
diff --git a/sdk/lib/_internal/lib/js_mirrors.dart b/sdk/lib/_internal/lib/js_mirrors.dart
index 2f2069bbae94b08857ad4d2f14612a64299a0fd1..1bb198c6a4254cd9e2f66c0b892615ba3f2331b1 100644
--- a/sdk/lib/_internal/lib/js_mirrors.dart
+++ b/sdk/lib/_internal/lib/js_mirrors.dart
@@ -488,6 +488,9 @@ class JsLibraryMirror extends JsDeclarationMirror with JsObjectMirror
   // TODO(ahe): Implement this.
   Function operator [](Symbol name)
       => throw new UnimplementedError();
+
+  List<LibraryDependencyMirror> get libraryDependencies
+      => throw new UnimplementedError();
 }
 
 String n(Symbol symbol) => _symbol_dev.Symbol.getName(symbol);