Use entities in most of MirrorsData

pkg/compiler/lib/src/kernel/env.dart

Index: pkg/compiler/lib/src/kernel/env.dart
diff --git a/pkg/compiler/lib/src/kernel/env.dart b/pkg/compiler/lib/src/kernel/env.dart
index 2c31f77596a72cd20eaa76689ca41c6a5fa87658..f861770f36e2dc0830b0849295ccdf76cbf47873 100644
--- a/pkg/compiler/lib/src/kernel/env.dart
+++ b/pkg/compiler/lib/src/kernel/env.dart
@@ -146,6 +146,21 @@ class LibraryEnv {
   }
 }
 
+class LibraryData {
+  final ir.Library library;
+  Iterable<ConstantValue> _metadata;
+
+  LibraryData(this.library);
+
+  Iterable<ConstantValue> getMetadata(KernelToElementMapBase elementMap) {
+    return _metadata ??= elementMap.getMetadata(library.annotations);
+  }
+
+  LibraryData copy() {
+    return new LibraryData(library);
+  }
+}
+
 /// Environment for fast lookup of class members.
 class ClassEnv {
   final ir.Class cls;