Recompute librariesByName after loading a deferred library.

tests/lib/mirrors/deferred_mirrors_update_test.dart

Index: tests/lib/mirrors/deferred_mirrors_update_test.dart
diff --git a/tests/lib/mirrors/deferred_mirrors_update_test.dart b/tests/lib/mirrors/deferred_mirrors_update_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..6aa074d799fc3d35bba0dcd1390e9d1ec7dc71ff
--- /dev/null
+++ b/tests/lib/mirrors/deferred_mirrors_update_test.dart
@@ -0,0 +1,17 @@
+library main;
+
+// Test that the library-mirrors are updated after loading a deferred library.
+
+@MirrorsUsed(targets: "D")
+import "dart:mirrors";
+
+import "deferred_mirrors_update_lib.dart" deferred as l;
+
+class D {}
+
+void main() {
+  print(reflectClass(D).owner);
+  l.loadLibrary().then((_) {
+    l.foo();
+  });
+}