Use configurations and declared variables to select import/export URIs during prelinking.

pkg/analyzer/test/src/summary/summary_common.dart

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library analyzer.test.src.summary.summary_common;
 
 import 'package:analyzer/analyzer.dart';
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/error/listener.dart';
@@ skipping 6044 matching lines @@
     expect(linked.exportNames, hasLength(1));
     checkExportName(linked.exportNames[0], absUri('/a.dart'), 'a.dart', 'C',
         ReferenceKind.classOrEnum);
   }
 
   test_export_configurations() {
     if (!checkAstDerivedData) {
       // Element model does not provide access to configurations.
       return;
     }
-    addNamedSource('/foo.dart', 'bar() {}');
-    addNamedSource('/foo_io.dart', 'bar() {}');
-    addNamedSource('/foo_html.dart', 'bar() {}');
+    addNamedSource('/foo.dart', 'class A {}');
+    addNamedSource('/foo_io.dart', 'class A {}');
+    addNamedSource('/foo_html.dart', 'class A {}');
     String libraryText = r'''
 export 'foo.dart'
   if (dart.library.io) 'foo_io.dart'
   if (dart.flavor == 'html') 'foo_html.dart';
+
+class B extends A {}
 ''';
     serializeLibraryText(libraryText);
     UnlinkedExportPublic exp = unlinkedUnits[0].publicNamespace.exports[0];
     expect(exp.configurations, hasLength(2));
     {
       UnlinkedConfiguration configuration = exp.configurations[0];
       expect(configuration.name, 'dart.library.io');
       expect(configuration.value, 'true');
       expect(configuration.uri, 'foo_io.dart');
     }
@@ skipping 4467 matching lines @@
 class _PrefixExpectation {
   final ReferenceKind kind;
   final String name;
   final String absoluteUri;
   final String relativeUri;
   final int numTypeParameters;
 
   _PrefixExpectation(this.kind, this.name,
       {this.absoluteUri, this.relativeUri, this.numTypeParameters: 0});
 }