Use unitMember/classMember/parameter names instead of offsets in index.

pkg/analyzer/lib/src/summary/idl.dart

Index: pkg/analyzer/lib/src/summary/idl.dart
diff --git a/pkg/analyzer/lib/src/summary/idl.dart b/pkg/analyzer/lib/src/summary/idl.dart
index 505ade8855078f11d43b869fa4e25538db8d00fb..60a0552f6e6048c4abd55fdd5bb052e9390fa8f6 100644
--- a/pkg/analyzer/lib/src/summary/idl.dart
+++ b/pkg/analyzer/lib/src/summary/idl.dart
@@ -714,12 +714,32 @@ abstract class PackageIndex extends base.SummaryClass {
 
   /**
    * Each item of this list corresponds to a unique referenced element.  It is
-   * the offset of the element name relative to the beginning of the file.  The
-   * list is sorted in ascending order, so that the client can quickly check
-   * whether an element is referenced in this [PackageIndex].
+   * the identifier of the class member element name, or `null` if the element is
+   * a top-level element.  The list is sorted in ascending order, so that the
+   * client can quickly check whether an element is referenced in this
+   * [PackageIndex].
+   */
+  @Id(7)
+  List<int> get elementNameClassMemberIds;
+
+  /**
+   * Each item of this list corresponds to a unique referenced element.  It is
+   * the identifier of the named parameter name, or `null` if the element is not
+   * a named parameter.  The list is sorted in ascending order, so that the
+   * client can quickly check whether an element is referenced in this
+   * [PackageIndex].
+   */
+  @Id(8)
+  List<int> get elementNameParameterIds;
+
+  /**
+   * Each item of this list corresponds to a unique referenced element.  It is
+   * the identifier of the top-level element name, or `null` if the element is
+   * the unit.  The list is sorted in ascending order, so that the client can
+   * quickly check whether an element is referenced in this [PackageIndex].
    */
   @Id(1)
-  List<int> get elementOffsets;
+  List<int> get elementNameUnitMemberIds;
 
   /**
    * Each item of this list corresponds to a unique referenced element.  It is