Add metadata annotations to library definitions.

runtime/vm/kernel.h

Index: runtime/vm/kernel.h
diff --git a/runtime/vm/kernel.h b/runtime/vm/kernel.h
index 65289c60fc3e8cd234479a1725b70c395426dd97..a66e9b82f3f5285213111f4485fb9cb2f29a3c33 100644
--- a/runtime/vm/kernel.h
+++ b/runtime/vm/kernel.h
@@ -474,6 +474,7 @@ class Library : public LinkedNode {
   StringIndex import_uri() { return import_uri_index_; }
   intptr_t source_uri_index() { return source_uri_index_; }
   StringIndex name() { return name_index_; }
+  List<Expression>& annotations() { return annotations_; }
   List<LibraryDependency>& dependencies() { return dependency_; }
   List<Typedef>& typedefs() { return typedefs_; }
   List<Class>& classes() { return classes_; }
@@ -492,6 +493,7 @@ class Library : public LinkedNode {
   StringIndex name_index_;
   StringIndex import_uri_index_;
   intptr_t source_uri_index_;
+  List<Expression> annotations_;
   List<LibraryDependency> dependency_;
   List<Typedef> typedefs_;
   List<Class> classes_;