Introduce code to resynthesize element models from summaries.

pkg/analyzer/lib/dart/element/element.dart

Index: pkg/analyzer/lib/dart/element/element.dart
diff --git a/pkg/analyzer/lib/dart/element/element.dart b/pkg/analyzer/lib/dart/element/element.dart
index 64b87f3e05a182bcdec38ed401d882c92b7baa2e..7d74842687f108e57f674b96781e9d951811b1b5 100644
--- a/pkg/analyzer/lib/dart/element/element.dart
+++ b/pkg/analyzer/lib/dart/element/element.dart
@@ -538,9 +538,9 @@ abstract class Element implements AnalysisTarget {
    * Elements with a smaller offset will be sorted to be before elements with a
    * larger name offset.
    */
-  static final Comparator<Element> SORT_BY_OFFSET =
-      (Element firstElement, Element secondElement) =>
-          firstElement.nameOffset - secondElement.nameOffset;
+  static final Comparator<Element> SORT_BY_OFFSET = (Element firstElement,
+          Element secondElement) =>
+      firstElement.nameOffset - secondElement.nameOffset;
 
   /**
    * Return the analysis context in which this element is defined.
@@ -1307,6 +1307,12 @@ abstract class LibraryElement implements Element {
   bool get hasLoadLibraryFunction;
 
   /**
+   * Return an identifier that uniquely identifies this element among the
+   * children of this element's parent.
+   */
+  String get identifier;
+
+  /**
    * Return a list containing all of the libraries that are imported into this
    * library. This includes all of the libraries that are imported using a
    * prefix (also available through the prefixes returned by [getPrefixes]) and